Grade 12
/ Annals on sequences 22 exercises (including 21 corrected)
- Suite studies (7 exercices)
- Suites, variations and limits (8 exercices)
- Suites and logarithms (4 exercices)
- Suites and integrations (2 exercices)
E.5079
Part
A
Consider
the
function
f
,
taken
from
an
algorithm,
and
whose
argument
is
a
natural
number.
Function
f(N)
U
←
0
For
k
ranging
from
0
to
N
−
1
U
←
3
·
U
−
2
·
k+3
End
To
Return
U
What
is
the
value
returned
by
this
function
when
called
with
the
value
3
for
the
argument
N
?
Part
B
y
Consider
the
sequence
u
n
defined
by
u
0
=0
and,
for
any
integer
nature
n
:
u
n
+1
=
3
·
u
n
−
2
·
n
+
3
1
Calculate
u
1
and
u
2
.
2
a
Demonstrate
by
recurrence
that,
for
any
natural
number
n
:
u
n
n
b
Deduce
the
limit
of
the
sequence
u
n
.
3
Demonstrate
that
the
sequence
u
n
is
increasing.
4
Let
the
sequence
v
n
be
defined,
for
any
natural
number
n
,
by
v
n
=
u
n
−
n
+
1
a
Demonstrate
that
the
sequence
v
n
is
a
geometric
se-quence.
b
Deduce
that,
for
any
natural
number
n
:
u
n
=
3
n
+
n
−
1
5
Let
p
be
a
non-zero
natural
number.
a
Why
can
we
say
that
there
exists
at
least
one
integer
n
0
such
that,
for
any
n
n
0
,
u
n
10
p
?
We
are
now
interested
in
the
smallest
integer
n
0
.
b
Justify
that
:
n
0
3
·
p
.
c
Using
the
calculator,
determine
this
integer
n
0
for
the
value
p
=3
.
d
Propose
a
function
which,
for
a
value
p
passed
as
an
argument,
returns
the
value
of
the
smallest
integer
n
0
such
that,
for
any
n
n
0
,
we
have
u
n
10
p
.
E.5019
1
Consider
the
function
f
,
given
below
and
derived
from
an
algorithm,
taking
the
arguments
a
,
b
,
N
of
non-zero
integer
values
:
Function
f(a,b,N)
u
←
a
v
←
b
n
←
0
As
long
as
n<N
n
←
n+1
u
←
a
+
b
2
v
←
a
2
+
b
2
2
a
←
u
b
←
v
.
End
As
long
as
Renvoyer
(
u
;
v)
Reproduce
and
complete
the
following
table,
showing
the
values
taken
by
the
function
variables
f
during
step-by-step
execution
and
when
the
the
call
is
made
with
the
values
a
=4
,
b
=9
and
N
=2
.
Successive
values
of
u
and
v
will
be
rounded
to
the
thousandth.
n
a
b
u
v
0
4
9
1
2
In
the
following,
a
and
b
are
two
real
numbers
such
that
0
<a<b
.
Consider
the
sequences
u
n
and
v
n
defined
by:
u
0
=
a
,
v
0
=
b
and,
for
any
natural
number
n
:
u
n
+1
=
u
n
+
v
n
2
;
v
n
+1
=
u
2
n
+
v
2
n
2
2
a
Demonstrate
by
recurrence
that,
for
any
natural
number
n
,
we
have
:
u
n
>
0
;
v
n
>
0
b
Demonstrate
that,
for
any
natural
number
n
:
v
2
n
+1
−
u
2
n
+1
=
u
n
−
v
n
2
2
Deduce
that,
for
any
natural
number
n
,
we
have
:
u
n
v
n
.
3
a
Demonstrate
that
the
sequence
u
n
is
increasing.
b
Compare
v
2
n
+1
and
v
2
n
.
Deduce
the
direction
of
varia-tion
of
the
sequence
v
n
.
https://chingmath.fr
chapExoCorrec/5079
sacados/5079
Polynesie 2012
5 points
chapExoCorrec/5019
sacados/5019
Asie
Juin 2012
5 points
-3-2-123456I-1234567JOCf
E.3836
Consider
the
sequence
of
real
num-bers
u
n
defined
on
N
by:
u
0
=
−
1
u
1
=
1
2
u
n
+2
=
u
n
+1
−
1
4
·
u
n
for
any
natural
number
n
.
1
Calculate
u
2
and
deduce
that
the
sequence
u
n
is
nei-ther
arithmetic
nor
geometric.
2
We
define
the
sequence
v
n
by
posing,
for
any
natural
number
n
:
v
n
=
u
n
+1
−
1
2
·
u
n
a
Calculate
v
0
.
b
Express
v
n
+1
as
a
function
of
v
n
.
c
Deduce
that
v
n
is
geometric
of
reason
1
2
.
d
Express
v
n
in
terms
of
n
.
3
We
define
the
sequence
w
n
by
posing,
for
any
natural
number
n
:
w
n
=
u
n
v
n
a
Calculate
w
0
.
b
Using
the
equality
u
n
+1
=
v
n
+
1
2
·
u
n
,
express
w
n
+1
as
a
function
of
u
n
and
v
n
.
c
Deduce
that
for
any
n
of
N
:
w
n
+1
=
w
n
+2
.
d
Express
w
n
as
a
function
of
n
.
4
Show
that
for
any
natural
number
n
:
u
n
=
2
·
n
−
1
2
n
5
For
any
natural
number
n
,
we
pose
:
S
n
=
k
=
n
k
=0
u
k
=
u
0
+
u
1
+
·
·
·
+
u
n
Demonstrate
by
recurrence
that
for
any
n
∈
N
:
S
n
=
2
−
2
n
+
3
2
n
E.3210
The
sequence
u
n
is
defined
by:
u
0
=
1
;
u
n
+1
=
1
2
u
n
+
n
−
1
for
all
n
∈
N
1
a
Show
that
for
any
n
3
:
u
n
0
.
b
Deduce
that
for
any
n
4
:
u
n
n
−
2
.
c
Deduce
the
limit
of
the
sequence
(
u
n
)
.
2
We
define
the
sequence
(
v
n
)
by:
v
n
=
4
u
n
−
8
n
+
24
a
Show
that
(
v
n
)
is
a
decreasing
geometric
sequence
whose
reason
and
first
term
will
be
given.
b
Show
that
for
any
natural
number
n
:
u
n
=
7
·
1
2
n
+
2
n
−
6
.
c
Verify
that
for
any
natural
number
n
,
u
n
=
x
n
+
y
n
où
(
x
n
)
is
a
geometric
sequence
and
(
y
n
)
an
arithmetic
se-quence
whose
first
term
and
reason
are
to
be
specified
for
each.
d
Deduce
the
expression
of
S
n
=
n
k
=0
u
k
as
a
function
of
n
.
E.3472
Consider
the
sequence
u
n
n
∈
N
defined
by:
u
0
=
1
u
n
+1
=
1
3
·
u
n
+
n
−
2
for
any
natural
number
n
.
1
Calculate
u
1
,
u
2
and
u
3
.
2
a
Demonstrate
that
for
any
natural
integer
n
4
:
u
n
0
.
b
Deduce
that
for
any
natural
number
n
5
:
u
n
n
−
3
c
Deduce
the
limit
of
the
sequence
u
n
n
∈
N
3
We
define
the
sequence
v
n
n
∈
N
by:
For
any
n
∈
N
:
v
n
=
−
2
·
u
n
+
3
·
n
−
21
2
.
a
Show
that
the
sequence
v
n
n
∈
N
is
a
geometric
se-quence
whose
reason
and
first
term
will
be
given.
b
Deduce
that
:
for
any
n
∈
N
:
u
n
=
25
4
·
1
3
n
+
3
2
·
n
−
21
4
.
c
Let
the
sum
S
n
be
defined
for
any
natural
integer
n
by:
S
n
=
n
k
=0
u
k
Determine
the
expression
of
S
n
as
a
function
of
n
.
2.
Suites,
variations
and
limits
E.3415
Consider
the
function
f
defined
on
−∞
;
6
by:
f
(
x
)
=
9
6
−
x
We
define
the
sequence
U
n
by:
U
0
=
−
3
;
U
n
+1
=
f
U
n
for
any
n
∈
N
1
The
representative
curve
of
the
function
f
is
given
be-low
accompanied
by
that
of
the
straight
line
of
equation
y
=
x
.
https://chingmath.fr
chapExoCorrec/3836
sacados/3836
Antilles-Guyanne
Septembre 2010
5 points
chapExoCorrec/3210
sacados/3210
Antilles-Guyane
Septembre 2005
5 points
chapExoCorrec/3472
sacados/3472
chapExoCorrec/3415
sacados/3415
-3-2-123456I-1234567JOCf
Construct,
in
the
above
reference
frame,
the
points
:
M
0
(
U
0
;
0)
;
M
1
(
U
1
;
0)
;
M
2
(
U
2
;
0)
;
M
3
(
U
3
;
0)
;
M
4
(
U
4
;
0)
What
conjectures
can
be
made
regarding
the
direction
of
variation
and
possible
convergence
of
the
sequence
U
n
?
2
a
Demonstrate
that
si
x<
3
then
9
6
−
x
<
3
.
Deduce
that
U
n
<
3
for
any
natural
number
n
.
b
Study
the
direction
of
variation
of
the
sequence
U
n
.
c
What
can
be
deduced
from
questions
2
a
and
2
b
?
3
Consider
the
sequence
V
n
defined
by
V
n
=
1
U
n
−
3
for
any
natural
number
n
.
a
Demonstrate
that
the
sequence
V
n
is
an
arithmetic
sequence
of
reason
−
1
3
.
b
Determine
V
n
then
U
n
as
a
function
of
n
.
c
Calculate
the
limit
of
the
sequence
U
n
.
E.5864
Consider
the
sequence
u
n
de-fined
by
u
0
=
1
2
and
such
that
for
any
natural
number
n
:
u
n
+1
=
3
·
u
n
1
+
2
·
u
n
1
a
Calculate
u
1
and
u
2
.
b
Demonstrate,
by
recurrence,
that
for
any
natural
num-ber
n
:
0
<u
n
.
2
We
admit
that
for
any
natural
number
n
:
u
n
<
1
.
a
Demonstrate
that
the
sequence
u
n
is
increasing.
b
Demonstrate
that
the
sequence
u
n
converges.
3
Let
v
n
be
the
sequence
defined,
for
any
natural
number
n
by:
v
n
=
u
n
1
−
u
n
a
Show
that
the
sequence
v
n
is
a
geometric
sequence
of
reason
3
.
b
Express
for
any
natural
number
n
,
v
n
as
a
function
of
n
.
c
Deduce
that,
for
any
natural
number
n
:
u
n
=
3
n
3
n
+
1
d
Determine
the
limit
of
the
sequence
u
n
.
E.3474
Let
f
be
the
function
defined
on
the
interval
0
;
+
∞
by:
f
(
x
)
=
6
−
5
x
+
1
The
aim
of
this
exercise
is
to
study
sequences
u
n
defined
by
a
first
positive
or
zero
term
u
0
and
verifying
for
any
natural
number
n
:
u
n
+1
=
f
(
u
n
)
1
Study
of
function
properties
f
:
a
Study
the
direction
of
variation
of
the
function
f
on
the
interval
0
;
+
∞
.
b
Solve
in
the
interval
0
;
+
∞
the
equation
:
f
(
x
)
=
x
.
Note
¸
the
solution.
c
Show
that
if
x
belongs
to
the
interval
0
;
¸
,
then
f
(
x
)
belongs
to
the
interval
0
;
¸
.
Similarly,
show
that
if
x
belongs
to
the
interval
¸
;
+
∞
,
then
f
(
x
)
belongs
to
the
interval
¸
;
+
∞
.
2
Study
the
sequence
u
n
for
u
0
=0
:
In
this
question,
consider
the
sequence
u
n
defined
by
u
0
=0
and
for
any
natural
number
n
:
u
n
+1
=
f
u
n
=
6
−
5
u
n
+
1
a
On
the
graph
shown
in
Appendix
2,
are
represented
the
curves
with
equations
y
=
x
and
y
=
f
(
x
)
.
Place
the
point
A
0
of
coordinates
(
u
0
;
0)
,
and,
using
these
curves,
construct
from
A
0
the
points
A
1
,
A
2
,
A
3
and
A
4
with
ordinate
zero
and
abscissa
u
1
,
u
2
,
u
3
and
u
4
respectively.
What
conjectures
can
be
made
about
the
direction
of
variation
and
convergence
of
the
sequence
u
n
?
b
Demonstrate,
by
recurrence,
that
for
any
natural
num-ber:
0
u
n
u
n
+1
¸
.
c
Deduce
that
the
sequence
u
n
is
convergent
and
de-termine
its
limit.
3
Study
the
sequences
u
n
according
to
the
values
of
the
positive
or
zero
real
u
0
.
In
this
question,
any
trace
of
argumentation,
however
incomplete,
or
initiative,
however
unsuccessful,
will
be
taken
into
account
in
the
assessment.
What
can
be
said
about
the
direction
of
variation
and
convergence
of
the
sequence
u
n
depending
on
the
val-ues
of
the
positive
or
zero
real
u
0
?
https://chingmath.fr
chapExoCorrec/5864
sacados/5864
chapExoCorrec/3474
sacados/3474
23456789I23456789JOC
E.6269
Consider
the
numerical
sequence
u
n
defined
on
N
by:
u
0
=
2
;
u
n
+1
=
−
1
2
·
u
2
n
+
3
·
u
n
−
3
2
pour
tout
n
∈
N
Part
A
:
Conjecture
1
Calculate
the
exact
values,
given
in
irreducible
fractions,
of
u
1
and
u
2
.
2
Give
an
approximate
value
to
the
nearest
10
−
5
of
the
terms
u
3
and
u
4
.
3
Conjecture
the
direction
of
variation
and
convergence
of
the
sequence
u
n
.
Part
B:
Validation
of
conjectures
Consider
the
numerical
sequence
v
n
defined
for
any
natural
number
n
,
by:
v
n
=
u
n
−
3
1
Show
that,
for
any
natural
number
n
:
v
n
+1
=
−
1
2
·
v
2
n
.
2
Demonstrate
by
recurrence
that,
for
any
natural
number
n
:
−
1
v
n
0
.
3
a
Demonstrate
that,
for
any
natural
number
n
:
v
n
+1
−
v
n
=
−
v
n
·
1
2
·
v
n
+
1
.
b
Deduce
the
direction
of
variation
of
the
sequence
v
n
.
4
Why
can
we
then
say
that
the
sequence
v
n
converges?
5
We
note
‘
the
limit
of
the
sequence
v
n
.
We
admit
that
‘
belongs
to
the
interval
−
1
;
0
and
ver-ifies
the
equality:
‘
=
−
1
2
·
‘
2
.
Determine
the
value
of
‘
.
6
Are
the
conjectures
made
in
part
A
validated?
E.6763
Part
A
Let
u
n
be
the
sequence
defined
by
its
first
term
u
0
and,
for
any
natural
number
n
,
by
the
relation:
u
n
+1
=
a
·
u
n
+
b
(
a
and
b
real
non-zero
such
that
a
=1
)
We
pose,
for
any
natural
number
n
:
v
n
=
u
n
−
b
1
−
a
1
Demonstrate
that,
the
sequence
v
n
is
geometric
of
rea-son
a
.
2
Deduce
that
if
a
belongs
to
the
interval
−
1
;
1
,
then
the
sequence
u
n
has
limit
b
1
−
a
.
Part
B
In
March
2015
,
Max
buys
a
green
plant
measuring
80
cm
.
He
is
advised
to
prune
it
every
year,
in
March,
by
cutting
off
a
quarter
of
its
height.
The
plant
will
then
grow
by
30
cm
over
the
following
twelve
months.
As
soon
as
he
gets
home,
Max
prunes
his
plant.
1
How
tall
will
the
plant
be
in
March
2016
before
Max
prunes
it?
2
For
any
natural
number
n
,
let
h
n
be
the
height
of
the
plant,
before
it
is
pruned,
in
March
of
the
year
(2015+
n
)
.
a
Justify
that,
for
any
natural
number
n
:
h
n
+1
=
0.75
·
h
n
+
30
b
Use
the
calculator
to
conjecture
the
direction
of
varia-tion
of
the
sequence
h
n
.
Demonstrate
this
conjecture
(reasoning
by
recurrence
may
be
used)
.
c
Is
the
sequence
h
n
convergent?
Justify
the
answer.
https://chingmath.fr
23456789I23456789JOC
chapExoCorrec/6269
sacados/6269
chapExoCorrec/6763
sacados/6763
KWUV012
E.6962
The
aim
of
this
exercise
is
to
study
sequences
of
positive
terms
whose
first
term
u
0
is
strictly
greater
than
1
and
possessing
the
following
property:
for
any
natural
number
n>
0
,
the
sum
of
the
first
n
consecutive
terms
is
equal
to
the
product
of
the
first
n
consecutive
terms.
We
admit
that
such
a
sequence
exists
and
note
it
u
n
.
It
therefore
verifies
three
properties
:
u
0
>
1
for
any
n
0
,
u
n
0
for
all
n>
0
:
u
0
+
u
1
+
···
+
u
n
−
1
=
u
0
×
u
1
×···×
u
n
−
1
1
We
choose
u
0
=3
.
Determine
u
1
and
u
2
.
2
For
any
integer
n>
0
,
we
note
:
s
n
=
u
0
+
u
1
+
···
+
u
n
−
1
=
u
0
×
u
1
×···×
u
n
−
1
.
In
particular,
we
have
s
1
=
u
0
.
a
Verify
that
for
any
integer
n>
0
:
s
n
+1
=
s
n
+
u
n
and
s
n
>
1
b
Deduce
that
for
any
integer
n>
0
:
u
n
=
s
n
s
n
−
1
c
Show
that
for
any
n
0
:
u
n
>
1
.
3
The
function
f
below
is
desiredbelow
returns
the
value
of
one
of
the
terms
in
the
sequence
u
n
où
the
arguments
u
and
n
of
the
function
are
respectively
the
first
term
of
the
sequence
u
n
and
the
rank
of
the
desired
term.
Function
f(u,n)
s
←
u
For
i
from
1
to
n
u
←
...
s
←
...
End
for
Return
u
a
Copy
and
complete
the
processing
part
of
the
above
algorithm.
b
The
table
below
gives
values
rounded
to
the
thou-sandth
of
u
n
for
different
values
of
the
integer
n
:
n
0
5
10
20
30
40
u
n
3
1.140
1.079
1.043
1.030
1.023
What
conjecture
can
be
made
about
the
convergence
of
the
sequence
u
n
?
4
a
Justify
that
for
any
natural
number
n>
0
:
s
n
>n
.
b
Deduce
the
limit
of
the
sequence
s
n
and
then
that
of
the
sequence
u
n
.
E.5854
Let
two
sequences
u
n
and
v
n
be
defined
by
u
0
=2
and
v
0
=10
and
for
any
natural
number
n
:
u
n
+1
=
2
·
u
n
+
v
n
3
;
v
n
+1
=
u
n
+
3
·
v
n
4
Part
A
Consider
the
function
f
ex-tracted
from
an
algorithm
où
its
argument
n
is
an
integer
greater
than
or
equal
to
1
:
We
call
the
function
f
with
the
value
n
=2
as
its
argument.
Copy
and
complete
the
table
given
be-low
giving
the
state
of
the
vari-ables
during
this
call:
Function
f(n)
K
←
0
U
←
2
V
←
10
As
long
as
K<n
K
←
K+1
W
←
U
U
←
2
·
U+V
3
V
←
W
+
3
·
V
4
End
as
long
as
Renvoyer
(
U
;
V)
Part
B
1
a
Show
that
for
any
natural
number
n
:
v
n
+1
−
u
n
+1
=
5
12
·
v
n
−
u
n
b
For
any
natural
number
n
,
we
pose
:
w
n
=
v
n
−
u
n
.
Show
that
for
any
natural
number
n
:
w
n
=
8
·
5
12
n
.
2
a
Show
that
the
sequence
u
n
is
increasing
and
that
the
sequence
v
n
is
decreasing.
b
Deduce
from
the
results
of
questions
1
b
and
2
a
that
for
any
natural
number
n
,
we
have
:
u
n
10
;
v
n
2
c
Deduce
that
the
sequences
u
n
and
v
n
are
conver-gent.
3
Show
that
the
suites
u
n
and
v
n
have
the
same
limit.
4
Show
that
the
sequence
t
n
defined
by
t
n
=3
·
u
n
+4
·
v
n
is
constant.
Deduce
that
the
common
limit
of
the
sequences
u
n
and
v
n
is
46
7
https://chingmath.fr
chapExoCorrec/6962
sacados/6962
chapExoCorrec/5854
sacados/5854
KWUV012
E.5077
The
purpose
of
this
exercise
is
to
study
the
sequence
u
n
defined
by:
u
0
=
3
;
u
n
+1
=
1
2
·
u
n
+
7
u
n
pour
tout
n
∈
N
We
may
use
without
demonstration
the
fact
that
for
any
nat-ural
number
n
,
u
n
>
0
.
1
We
denote
by
f
the
focntion
defined
on
the
interval
0
;
+
∞
by:
f
(
x
)
=
1
2
·
x
+
7
x
(
∗
)
Show
that
the
function
f
admits
a
minimum.
Deduce
that
for
any
natural
number
n
:
u
n
√
7
2
a
Let
n
be
any
natural
number.
Study
the
sign
of
u
n
+1
−
u
n
.
b
Why
can
we
deduce
that
the
sequence
u
n
is
conver-gent?
c
From
the
relation
(
∗
)
we
deduce
that
the
limit
‘
of
this
sequence
is
such
that
:
‘
=
1
2
·
‘
+
7
‘
.
Determine
‘
.
3
Demonstrate
that
for
any
natural
number
n
:
u
n
+1
−
7
=
1
2
·
u
n
−
7
2
u
n
4
We
define
the
sequence
d
n
by:
d
0
=
1
;
d
n
+1
=
1
2
·
d
n
2
pour
tout
n
∈
N
a
Demonstrate
by
recurrence
that
for
any
natural
num-ber
n
:
u
n
−
7
d
n
b
Here’s
a
function
from
an
algorithm
taking
as
argu-ment
p
which
is
a
natural
integer.
Function
f(p)
d
←
1
n
←
0
As
long
as
d>10
−
p
d
←
0.5
·
d
2
n
←
n+1
End
As
long
as
Return
n
Calling
the
function
with
the
value
9
,
the
value
re-turned
is
the
number
5
.
What
inequality
can
be
deduced
for
d
5
?
?
Justify
that
u
5
is
an
approximate
value
of
7
to
the
nearest
10
−
9
.
3.
Suites
and
logarithms
E.5966
Part
A
Consider
the
sequence
u
n
defined
by:
u
0
=
2
;
u
n
+1
=
1
+
3
u
n
3
+
u
n
for
any
natural
number
n
All
terms
in
this
sequence
are
assumed
to
be
definite
and
strictly
positive.
1
Demonstrate
by
recurrence,
that
for
any
natural
number
n
,
we
have
:
u
n
>
1
2
a
Establish
that,
for
any
natural
number
n
,
we
have
:
u
n
+1
−
u
n
=
(1
−
u
n
)(1
+
u
n
)
3
+
u
n
b
Determine
the
direction
of
variation
of
the
sequence
u
n
.
Deduce
that
the
sequence
u
n
converges.
Part
B
Consider
the
sequence
u
n
defined
by:
u
0
=
2
;
u
n
+1
=
1
+
0.5
u
n
0.5
+
u
n
for
any
natural
number
n
.
All
terms
in
this
sequence
are
assumed
to
be
definite
and
strictly
positive.
1
Consider
the
following
algorithm:
u
←
2
For
i
ranging
from
1
to
n
u
←
1+0.5u
0.5+u
End
For
Reproduce
and
complete
the
table
below
showing
the
val-ues
taken
by
the
variables
i
and
u
during
the
step-by-step
execution
of
this
algorithm.
Values
of
u
will
be
rounded
to
the
thousandth.
i
1
2
3
u
2
For
n
=12
,
we
extended
the
previous
table
and
obtained
:
i
4
5
6
7
8
9
10
11
12
u
1.0083
0.9973
1.0009
0.9997
1.0001
0.99997
1.00001
0.999996
1.000001
Conjecture
the
behavior
of
the
sequence
u
n
at
infinity.
3
Consider
the
sequence
v
n
defined,
for
any
natural
num-ber
n
by:
v
n
=
u
n
−
1
u
n
+
1
a
Demonstrate
that
the
sequence
v
n
is
geometric
of
reason
−
1
3
.
b
Calculate
v
0
then
write
v
n
as
a
function
of
n
.
4
a
Show
that,
for
any
natural
number
n
,
we
have
:
v
n
=1
.
b
Show
that,
for
any
natural
number
n
,
we
have
:
u
n
=
1
+
v
n
1
−
v
n
c
Determine
the
limit
of
the
sequence
u
n
.
https://chingmath.fr
chapExoCorrec/5077
sacados/5077
Metropole
Septembre 2012
5 points
chapExoCorrec/5966
sacados/5966
E.6264
A
patient
is
given
a
drug
by
intra-venous
injection.
The
quantity
of
drug
in
the
blood
decreases
as
a
function
of
time.
The
aim
of
the
exercise
is
to
study,
for
different
hypotheses,
the
evolution
of
this
quantity
minute
by
minute.
1
At
time
0
an
injection
of
10
m‘
of
drug
is
made.
It
is
estimated
that
20
%
of
the
drug
is
eliminated
per
minute.
For
any
natural
number
n
,
note
u
n
the
amount
of
drug,
in
m‘
,
remaining
in
the
blood
after
n
minutes.
Thus,
u
0
=10
.
a
What
is
the
nature
of
the
sequence
u
n
?
b
For
any
natural
number
n
,
give
the
expression
of
u
n
as
a
function
of
n
.
c
After
how
long
does
the
amount
of
drug
remaining
in
the
blood
become
less
than
1
%
of
the
initial
amount?
Justify
the
answer.
2
At
time
0
,
a
machine
injects
10
m‘
of
drug.
It
is
esti-mated
that
20
%
of
the
drug
is
eliminated
per
minute.
When
the
amount
of
drug
falls
below
5
m‘
,
the
machine
re-injects
4
m‘
of
product.
After
15
minutes,
the
machine
is
stopped.
For
any
natural
number
n
,
note
v
n
the
amount
of
drug,
in
m‘
,
remaining
in
the
blood
at
minute
n
.
The
following
algorithm
makes
it
possible,
through
the
values
taken
by
the
variable
v
,
to
obtain
the
remaining
quantity
of
drug
minute
by
minute.
v
←
10
For
n
ranging
from
1
to
15
v
←
0.8
×
V
If
v<5
Then
v
←
v+4
End
If
End
For
a
Calculate
the
missing
elements
of
the
table
below
giv-ing,
rounded
to
10
−
2
and
for
n
greater
than
or
equal
to
1
,
the
remaining
minute-by-minute
quantity
of
drug
obtained
with
the
algorithm.
n
0
1
2
3
4
5
6
7
v
n
10
8
6.4
8.15
n
8
9
10
11
12
13
14
15
v
n
6.52
5.21
8.17
6.54
5.23
8.18
6.55
5.24
b
After
15
minutes,
what
total
amount
of
drug
has
been
injected
into
the
body?
c
We
want
to
program
the
machine
to
inject
2
m‘
prod-uct
when
the
amount
of
drug
in
the
blood
is
less
than
or
equal
to
6
m‘
and
that
it
stops
after
30
minutes.
Recopy
the
previous
algorithm,
modifying
it
so
that,
at
the
end
of
execution,
the
value
of
variable
b
is
the
quantity
of
drug,
in
m‘
,
remaining
in
the
blood
minute
by
minute
with
this
new
protocol.
3
The
machine
is
programmed
so
that
:
at
time
0
,
she
injects
10
m‘
of
medication,
every
minute,
she
injects
1
m‘
of
medication.
It
is
estimated
that
20
%
of
the
drug
in
the
blood
is
elim-inated
per
minute.
For
any
natural
number
n
,
note
w
n
the
amount
of
drug,
in
m‘
,
present
in
the
patient’s
blood
after
n
minutes.
a
Justify
that
for
any
natural
number
n
:
w
n
+1
=
0.8
·
w
n
+
1
.
b
For
any
natural
number
n
,
we
pose
:
z
n
=
w
n
−
5
.
Show
that
z
n
is
a
geometric
sequence
whose
reason
and
first
term
are
to
be
specified.
c
Deduce
the
expression
of
w
n
as
a
function
of
n
.
d
What
is
the
limit
of
the
sequence
w
n
?
What
inter-pretation
can
be
given?
E.3234
For
any
natural
number
n
,
we
pose
u
n
=
n
10
2
n
.
This
defines
a
sequence
u
n
n
∈
N
1
Prove,
for
any
non-zero
natural
number
n
,
the
following
equivalence
:
u
n
+1
0.95
u
n
if,
and
only
if,
1+
1
n
10
1.9
2
Consider
the
function
f
defined
on
1
;
+
∞
by:
f
(
x
)
=
1
+
1
x
10
a
Study
the
direction
of
variation
and
limit
in
+
∞
of
the
function
f
.
b
Show
that
there
exists
in
the
interval
1
;
+
∞
a
single
real
number
¸
such
that
f
(
¸
)=1.9
.
c
Determine
the
natural
number
n
0
such
that
n
0
−
1
¸
n
0
.
d
Show
that,
for
any
natural
number
n
greater
than
or
equal
to
16
,
we
have
:
1
+
1
n
10
1.9
.
3
a
Determine
the
direction
of
variation
of
the
sequence
(
u
n
)
from
rank
16
.
b
What
can
we
deduce
for
the
sequence?
4
Using
reasoning
by
recurrence,
prove,
for
any
natural
number
n
greater
than
or
equal
to
16,
the
framework:
0
u
n
0.95
n
−
16
·
u
16
Deduce
the
limit
of
the
sequence
u
n
n
∈
N
E.3267
1
Let
u
be
the
sequence
defined
by:
u
0
=
0
u
n
+1
=
1
2
−
u
n
for
any
natural
number
n
.
a
Calculate
u
1
,
u
2
and
u
3
.
Each
of
these
terms
will
be
expressed
as
an
irreducible
fraction.
b
Compare
the
first
four
terms
of
the
sequence
u
with
the
first
four
terms
of
the
sequence
w
defined
on
N
by:
w
n
=
n
n
+
1
.
c
Using
reasoning
by
recurrence,
show
that,
for
any
nat-ural
number
n
:
u
n
=
w
n
.
2
Let
v
be
the
sequence
with
general
term
v
n
defined
by:
v
n
=
ln
n
n
+
1
où
ln
denotes
the
neperian
logarithm
function
:
a
Show
that
:
v
1
+
v
2
+
v
3
=
−
ln
4
b
Let
S
n
be
the
sum
defined
for
any
non-zero
natural
number
n
by:
S
n
=
v
1
+
v
2
+
·
·
·
+
v
n
Express
S
n
as
a
function
of
n
.
Determine
the
limit
of
S
n
when
n
tends
to
+
∞
.
https://chingmath.fr
chapExoCorrec/6264
sacados/6264
chapExoCorrec/3234
sacados/3234
chapExoCorrec/3267
sacados/3267
4.
Suites
and
integrations
E.3161
Consider
the
sequences
u
n
and
v
n
defined,
for
any
non-zero
natural
number
n
,
by:
u
1
=
1
u
n
=
u
n
−
1
+
1
n
pour
n
2
;
v
n
=
u
n
−
ln
n
for
n
1
1
a
Calculate
u
2
,
u
3
and
u
4
.
b
Show
that,
for
any
non-zero
natural
number
n
:
u
n
=
n
k
=1
1
k
2
a
Show
that,
for
any
non-zero
natural
number
k
:
1
k
+
1
k
+1
k
1
x
d
x
1
k
b
Deduce
that,
for
any
integer
n
greater
than
or
equal
to
2
,
we
have
the
following
inequalities:
u
n
−
1
ln
n
u
n
−
1
n
;
0
v
n
1
3
a
Show
that,
for
any
non-zero
natural
number
n
:
v
n
+1
−
v
n
=
1
n
+
1
−
n
+1
n
1
x
d
x
b
Deduce
the
direction
of
variations
of
the
sequence
(
v
n
)
.
4
Show
that
the
sequence
(
v
n
)
converges.
We
note
‚
the
limit
of
the
sequence
(
v
n
)
(we
will
not
try
to
calculate
‚
)
.
What
is
the
limit
of
the
sequence
(
u
n
)
?
E.3144
1
For
any
non-zero
natural
number
n
,
consider
the
func-tion
f
n
defined
on
0
;
+
∞
by:
f
n
(
x
)
=
ln
x
+
x
n
−
1
a
Determine
the
limits
of
f
n
at
0
and
+
∞
then
study
the
direction
of
variations
of
f
n
.
b
Show
that
the
equation
f
n
(
x
)=0
admits
a
single
solu-tion
in
0
;
+
∞
.
Note
¸
n
this
solution.
Show
that
it
belongs
to
the
interval
1
;
e
.
2
The
plane
is
referred
to
an
orthonormal
reference
frame
O
;
−→
i
;
−→
j
;
−→
k
.
We
denote
(Γ)
the
representative
curve
of
the
neperian
logarithm
function.
a
Let
n
be
a
non-zero
natural
number.
Determine
an
equation
of
the
line
Δ
n
passing
through
the
point
A
of
coordinates
(0
;
1)
and
the
point
B
n
of
coordinates
(
n
;
0)
.
b
Make
a
sketch
representing
the
curve
(Γ)
and
the
straight
lines
Δ
1
,
Δ
2
and
Δ
3
.
c
Show
that
¸
n
is
the
abscissa
of
the
point
of
intersection
of
(Γ)
with
Δ
n
.
d
Specify
the
value
of
¸
1
then
make
a
conjecture
about
the
direction
of
variation
of
the
sequence
¸
n
)
.
3
a
Express
ln(
¸
n
)
as
a
function
of
n
and
¸
n
.
b
Express
f
n
+1
(
¸
n
)
as
a
function
of
n
and
¸
n
and
check
that
:
f
n
+1
(
¸
n
)
<
0
c
Deduce
from
the
previous
question
the
direction
of
variation
of
the
sequence
(
¸
n
)
.
d
Show
that
the
sequence
(
¸
n
)
converges.
Let
‘
be
its
limit.
Establish
that
ln
‘
=1
and
deduce
the
value
of
‘
.
4
We
denote
by
D
n
the
domain
bounded
by
the
curve
(Γ)
,
the
x-axis
and
the
straight
lines
of
equation
:
x
=
¸
n
and
x
=e
.
a
Calculate
the
area
of
the
domain
D
n
as
a
function
of
¸
n
and
show
that
this
area
is
equal
to
¸
2
n
n
.
b
Establish
that
:
(e
−
¸
n
)ln
¸
n
¸
2
n
n
(e
−
¸
n
)
c
Deduce
a
frame
for
n
(e
−
¸
n
)
.
d
is
the
general
term
sequence
n
(e
−
¸
n
)
convergent?
Does
this
result
allow
us
to
appreciate
the
speed
of
convergence
of
the
sequence
(
¸
n
)
?
5.
Unclassified
financial
years
E.8144
Polynesia
June
2018
https://chingmath.fr
chapExoCorrec/3161
sacados/3161
chapExoCorrec/3144
sacados/3144
sacados/8144