Outside the high school program / Homographic functions 17 exercises corrected

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1. Homographic functions E.407 Consider the function f defined by: f : x ↦−→ 3 x + 1 x − 3 1 Show that, for any x ∈ R \ 3 , we have : 3 x + 1 x − 3 = 3 + 10 x − 3 2 Determine the direction of variation of the function f on the interval −∞ ; 3 . E.424 Consider the function : f : x ↦−→ 3 x + 1 2 x − 1 1 a Establish the following equality: 3 x + 1 2 x − 1 = 5 4 x − 2 + 3 2 b Establish the decay of the function f on the interval −∞ ; 1 2 . 2 The representative curve of the function f is plotted in the orthonormal frame below : a Graphically, determine an approximate value of the antecedent of the number 3 by the function f . b Algebraically, find the antecedent of the number 3 by the function f . c Graphically, determine the solutions of the inequation f ( x ) 3 E.427 Consider the function f defined by the relation: f : x ↦−→ 2 − 6 x 1 − 2 x . 1 Give the definition set of the function f . 2 Determine the value of the reals a and b verifying: 2 − 6 x 1 − 2 x = a 1 − 2 x + b 3 Deduce that the function f is decreasing on 1 2 ; + ∞ E.429 Consider the function f defined by: f : x ↦−→ 2 x − 1 x + 1 1 Find the domain of the function f 2 Prove the following equality: 2 x − 1 x +1 =2+ − 3 x +1 3 Show the growth of the function f on ] −∞ ; − 1[ and also on ] − 1 ; + ∞ [ 4 Show algebraically that 2 has no antecedent under the function x . E.4868 Consider the function f defined by: f ( x ) = 6 · x − 7 3 − 2 · x 1 Establish the following equality: f ( x ) = − 3 + 2 3 − 2 · x 2 Establish the direction of variation of the function f on the interval −∞ ; 3 2 . 3 Determine the set of antecedents of 1 by the function f . 4 Solve the equation : f ( x ) = 2 · x E.419 Consider the function f defined by: f : x ↦−→ x + 1 x − 2 1 a Give the definition set of the function f . b Determine the image of 3 by the function f . c Determine the antecedents, for the function f , of the numbers − 1 and 0 . d Justify that 1 admits no antecedent by the function f . 2 Establish for any x ∈ R \ 2 , the following equality: x + 1 x − 2 = 3 x − 2 + 1 2. Homographic and affine functions E.6053 Consider the function f defined on R \{− 1 } by the relation: f ( x ) = x − 3 x + 1 In the reference frame O ; I ; J given below, we have plotted the curve C f representative of the function f . https://chingmath.fr chapExoCorrec/407 sacados/407 chapExoCorrec/424 sacados/424 -4-3-2-12345I-2-12345JOCf chapExoCorrec/427 sacados/427 chapExoCorrec/429 sacados/429 chapExoCorrec/4868 sacados/4868 chapExoCorrec/419 sacados/419 chapExoCorrec/6053 sacados/6053
1 a Determine the coordinates of the two points A and B on the curve C f with abscissa 1 and 3 respectively. b Determine the reduced equation of the line ( AB ) . c Tracer, dans le repère, la droite ( AB ) . 2 Consider the straight line (Δ) with reduced equation : (Δ): y = 3 x − 4 a Establish the following factorization : − 3 x 2 + 2 x + 1 = (1 − x )(3 x + 1) b Solve algebraically the inequation : f ( x ) 3 x − 4 c Deduce the relative position of the curve C f relative to the straight line (Δ) . d Draw the straight line (Δ) in the reference frame. E.6054 Consider the function f defined on R \{− 1 } by the relation: f ( x ) = 3 x + 1 x + 1 In the reference frame O ; I ; J given below, we have plotted the curve C f representative of the function f . 1 Determine the reduced equation of the line ( d ) passing through the two points of the curve C f having respec-tively abscissae − 2 3 and 1 . 2 Consider the straight line (Δ) with reduced equation : (Δ): y = x + 1 3 a Establish the following factorization : − 3 x 2 + 5 x + 2 = (2 − x )(3 x + 1) b Solve algebraically the inequation : f ( x ) x + 1 3 c Deduce the relative position of the curve C f relative to the straight line (Δ) on R . E.6052 Consider the function f defined on R \{− 1 } by the relation: f ( x ) = x − 3 x + 1 In the reference frame O ; I ; J given below, we have plotted the curve C f representative of the function f . 1 a Determine the coordinates of the two points A and B on the curve C f with abscissa − 2 and 3 respectively. b Determine the reduced equation of the line ( AB ) . c Tracer, dans le repère, la droite ( AB ) . 2 Consider the straight line (Δ) with reduced equation : (Δ): y = − 2 x − 3 a Algebraically determine the solutions of the equation : f ( x ) − 2 x − 3 b Deduce the relative position of the curve C f relative to the straight line (Δ) . c Draw the straight line (Δ) in the reference frame. 3. Homographic functions: problems https://chingmath.fr -6-4-2246I-6-4-224JOCf chapExoCorrec/6054 sacados/6054 xxyyCf(d chapExoCorrec/6052 sacados/6052 -6-4-2246I-4-2246JOCf
E.2987 A motorist travels on departmental roads a distance of 48 km at an average speed of 64 km = h , then trav-els the remaining x km on the freeway at an average speed of 115 km = h . 1 Determine the duration of your journey on departmental roads. 2 a Justify that the total travel time was : t = 3 4 + x 115 b Justify that the average speed v of the motorist, over the entire route, is written as a function of x : v = 460 x + 22080 4 x + 345 3 The driver knows that he has covered the entire route at an average speed of 92 km = h . Determine the distance travelled on the freeway by the driver. Then give the total distance of his journey. E.2989 In a plane with an orthonormal coordinate system ( O ; I ; J ) , consider the point A with coor-dinate (2 ; 1) . For a a real number belonging to the interval 2 ; + ∞ , con-sider the point M with coordinates ( a ; 0) . Note N the point of intersection of the line ( MA ) with the y-axis and note b the ordinate of the point N . We note P the point with coordinates ( a ; b ) . The graph below represents these different points in the case a =4 : The purpose of this exercise is to know the position of the point P as a function of the value a ; we speak of the ˇ locus géométrique ı of the point P when the number a describes the interval 2 ; + ∞ . Part A : 1 Justify that the point N cannot be defined for a =2 . 2 We’re interested in the position of point P when a =3 : a Place the point M 3 (3 ; 0) . b Place the point N 3 as indicated in the statement. What is the ordinate of the point N 3 ? c Place the point P 3 as specified in the statement. 3 Carry out the same procedure as for the previous ques-tion for the different values of a : a = 2.5 ; a = 5 ; a = 7 4 What conjecture can be made about the curve formed by the set of points P when the number a describes the interval 2 ; + ∞ ? Part B: 1 Justify that the directrix of the line ( MN ) is : 1 2 − a 2 Determine the reduced equation of the line ( MN ) 3 Determine the expression of b as a function of a . 4 Express the coordinates of point P as a function of a . Confirm the conjecture made in question A . E.2990 4. Studies of other functions E.3002 Consider the function f defined by the relation: f ( x ) = 1 x − 3 − 1 x + 1 1 Give the definition set of the function f . 2 Establish the following equalities: f ( x ) = 4 ( x − 3)( x + 1) = 4 ( x − 1) 2 − 4 3 a Justify that, for x belonging to −∞ ; − 1 , the image of x is positive. b Establish that the function f is increasing on − ∞ ; − 1 . 4 In a frame of reference O ; I ; J orthonormal, note C f the representative curve of the function f : a For any number h ∈ R such that the two numbers 1+ h and 1 − h belong to D f , verify the following equality: f (1 − h ) = f (1+ h ) b Displaying the curve C f on your calculator, what geo-metric property does the curve C f seem to possess? https://chingmath.fr chapExoCorrec/2987 sacados/2987 chapExoCorrec/2989 sacados/2989 -12345678I-12345JOAM4N4P4 sacados/2990 xyMINxyMINxyMSIN chapExoCorrec/3002 sacados/3002
E.3025 1 Consider the function f whose image of a number x is given by the relation: f ( x ) = x + 2 (2 x − 1)(3 − x ) a Determine the definition set of the function f b Establish the following equality: f ( x ) = 1 2 x − 1 + 1 3 − x c Show that for any x ∈ −∞ ; − 2 , the image of x by f is a positive number. 2 Let g be the function defined by: g : x ↦−→ 4 4 x − 2 − 2 2 x + 5 a Determine the definition set of the function g . b Determine the values of a and b verifying the following relationship : g ( x ) = 12 4 · ( x − a ) 2 + b c Establish the direction of variation of the function g on the interval 1 2 ; + ∞ E.440 1 Establish the equalities: a 1 + 2 x + 1 = x + 3 x + 1 pour x = − 1 . b 3 x 2 − 7 x + 6 x − 1 = 3 x − 4 + 2 x − 1 pour x =1 . c 1 x + 1 + 1 x − 1 = 2 x x 2 − 1 pour x =1 and x = − 1 . 2 Using the results of the previous question, establish the following statements : a The function f defined by x ↦−→ x +3 x +1 is decreasing on − 1 ; + ∞ . b The function g defined by x ↦−→ 2 x x 2 − 1 is increasing on 1 ; + ∞ . 5. Unclassified financial years E.7333 Consider the function f defined on R \{ 1 } by the relation: f ( x ) = 3 · x + 4 x − 1 1 Establish identity: f ( x )=3+ 7 x − 1 2 Establish that the function f is decreasing on the interval 1 ; + ∞ . E.4517 Consider the homographic function f defined by: f ( x ) = x − 2 4 x + 2 Consider the plane equipped with the coordinate system ( O ; I ; J ) orthonormal represented below : 1 Justify that the function f is defined on R \ − 1 2 : 2 Using a calculator: a Draw up a table of variations for the function f . b Complete the table of values, to the nearest tenth : x − 4 − 3 − 2 − 1.5 − 1 − 0.8 f ( x ) x − 0.3 0 0.5 1 2 3 4 f ( x ) 3 Plot the curve C f representing the function f in the co-ordinate system above. E.7465 Consider the function f defined on − 2 ; + ∞ by the relation: f ( x )= 3 · x +8 x +2 1 Establish identity: f ( x )=3+ 2 x +2 2 Establish that the function f is decreasing on − 2 ; + ∞ . https://chingmath.fr chapExoCorrec/3025 sacados/3025 chapExoCorrec/440 sacados/440 chapExoCorrec/7333 sacados/7333 chapExoCorrec/4517 sacados/4517 -4-3-2-1234I-3-2-123JO chapExoCorrec/7465 sacados/7465