Outside the high school program / Algebra: second degree reduced to first degree 25 exercises (including 22 corrected)

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8cm 1. Second degree: canonical form E.600 We will focus on second-degree polynomi-als : functions of the form x ↦→ a · x 2 + b · x + c with a , b , and c being fixed real numbers. We accept the following proposi-tion : Proposition: Any second-degree polynomial function can be written in the form : ¸ · ( x + ˛ ) 2 + This form is called the canonical form . First method 1 a Expand each of the remarkable identities below : a (2 x + 1) 2 b (3 2 x ) 2 c (3 x + 7) 2 d ( 4 x + 1) 2 b Deduce the canonical form of each of these second-degree polynomials: a 9 x 2 + 42 x 5 b 4 x 2 12 x + 16 c 4 x 2 + 4 x 8 d 16 x 2 8 x + 7 2 Using this method, deduce the reduced form of 25 x 2 + 20 x +7 . Second method Consider the equality: a · x 2 + b · x + c = ¸ · x + ˛ 2 + 1 Show that the numbers ¸ , ˛ , and must satisfy the fol-lowing system : ¸ = a 2 · ¸ · ˛ = b + ¸ · ˛ 2 = c We assume that for any value of the triplet ( a ; b ; c ) , the previous system has a unique solution. 2 For each of the following functions, determine the values of ¸ , ˛ and : a : x ↦− x 2 + 8 x 9 ; b : x ↦− 2 x 2 + 12 x + 4 c : x ↦− 6 x 2 + 6 x + 7 ; d : x ↦− 2 x 2 + 3 x 4 Bonus question 1 Show that for any numbers a , b , and c such that a =0 , we have : a · x 2 + b · x + c = a · x + b 2 a 2 b 2 4 ac 4 a 2 What can you say about the equation a · x 2 + b · x + c =0 si b 2 4 ac< 0 3 We accept the fact that : a · x 2 + b · x + c = a · x + b + b 2 4 ac 2 a x + b b 2 4 ac 2 a Give the two solutions to the equation 2 x 2 +4 x +1=0 E.2009 We are interested in equations of the form : ( E ) : ( x + ˛ ) 2 = 0 1 a Factor: ( x + 2) 2 9 . b Solve the following equation : ( x +2) 2 9=0 . 2 For each of the following equations, give the set of solu-tions : a ( x 7) 2 3 = 0 b ( x + 1) 2 + 2 = 0 c ( x 8) 2 = 0 3 Which condition must verify for : a ( E ) admits two solutions ; b ( E ) admits a single solution ; c ( E ) admits no solution. E.6035 In a cylinder, whose base has a radius of 8 cm , a ball is placed. We need to pour 104 cm 3 of oil into the cylin-der to just cover the ball. Determine the radius of the ball. E.4454 Establish the following equalities: a ( x + 2) 2 4 = x 2 + 4 x b ( x 9) 2 + 11 = x 2 18 x + 92 d ( x + 3) 2 12 = x 2 + 6 x 3 e 2( x + 1) 2 + 4 = 2 x 2 + 4 x + 6 E.4457 For each of the following equalities, give the value of ¸ (without justification) , then verify the proposed equality: a ( x + 2) 2 5 = x 2 + ¸ · x 1 b ( x 3) 2 + 7 = x 2 6 x + ¸ c 2( x + 1) 2 9 = ¸ · x 2 + 4 x 7 d 7( x 2) 2 + 1 = 7 x 2 + ¸ · x + 29 e ( x 5) 2 + ¸ = x 2 10 x + 10 f 3( x + ¸ ) 2 + 4 = 3 x 2 + 48 x + 196 2. Algebraic expressions https://chingmath.fr sacados/600 sacados/2009 sacados/6035 8cm chapExoCorrec/4454 sacados/4454 chapExoCorrec/4457 sacados/4457
E.435 Consider the following algebraic ex-pression : E = ( x + 1)(2 x 1) 1 Based on the reduced expanded form of the expression E , answer the following questions : a Find the coefficient of the term x 2 . b Find the numerical term. 2 Justify that the expression E is not equal to either of the following two expressions : F = 4 x 2 + x 1 ; G = 2( x + 1) 2 + 1 E.441 Consider the function f defined by: f ( x ) = 6 x 2 + 10 x 4 1 Establish the following equalities: f ( x ) = 2( x 1)(2 3 x ) = 6 x 5 6 2 + 1 6 2 Calculate the image of the numbers below by the func- tion f a 0 b 2 3 c 5 6 E.3001 Answer the following questions with-out justification : 1 Consider the polynomial P =2 · (2 x 1)(3 x )( x +2) : a Give, without justification, the coefficient of the de-gree term 3 of the polynomial P and the value of its numerical term. b Which of the polynomials below is the expanded and reduced form of the polynomial P ? 4 x 3 + 6 x 2 + 22 x + 12 4 x 3 + 6 x 2 + 22 x 12 4 x 3 + 6 x 2 + 22 x 12 4 x 3 + 6 x 2 + 22 x + 12 2 Determine the value of a , a real number, verifying the following equality: (2 x + 1)(3 x 2 + a · x + 1) = 6 x 3 7 x 2 3 x + 1 3. Equations E.4404 Solve the following inequations : a (2 x + 1)( x + 2) < 0 b (3 x )(2 x + 1) 0 c (5 x + 1)( x 2) > (3 + x )( x 2) d ( x + 3)(5 x ) 2( x + 3) E.4453 Solve the following inequations : a ( x + 2)( x 3) > 0 b ( x + 2)(5 3 x ) + ( x + 2)( x 2) 0 c (2 x + 1)(3 x 1) + (6 x + 3)(3 x 1) 0 d (2 3 x )( x 5) + 2(10 2 x ) < 0 E.4452 Complete the table of signs for each of the expressions E : 1 x −∞ 3 1 2 + 2 x + 1 0 3 + x 0 E =(2 x +1)(3+ x ) 0 0 2 x −∞ 3 4 2 + x 2 4 x 3 E =( x 2)(4 x 3) 3 x −∞ + 2 + x 2 x E = 2+ x 2 x E.9424 Solve the following inequalities: a 3 2 x 3 x + 1 > 0 b 3 x + 1 x + 1 < x + 1 4 x + 2 https://chingmath.fr chapExoCorrec/435 sacados/435 chapExoCorrec/441 sacados/441 chapExoCorrec/3001 sacados/3001 chapExoCorrec/4404 sacados/4404 chapExoCorrec/4453 sacados/4453 chapExoCorrec/4452 sacados/4452 chapExoCorrec/9424 sacados/9424
E.4409 Let ( E ) be the second-degree poly-nomial: ( E ): x 2 +4 x 12 1 Determine the canonical form of a Justify that the polynomial ( E ) admits as canonical form : ( x +2) 2 16 . b Justify that the polynomial ( E ) admits for minimum 16 . 2 a Deduce from question 1 a the factorized form of the polynomial ( E ) . b Deduce the two roots of the polynomial ( E ) . 3 Draw up the table of variations of the function f defined by: f ( x ) = x 2 + 4 x 12 4. Canonical form and extremums E.4407 Consider the expression 2 x 2 +8 x + 1 : 1 Establish the following equality: 2 x 2 + 8 x + 1 = 2( x 2) 2 + 9 2 Deduce that this expression reaches its maximum at x =2 . What is its maximum value? E.8516 1 Determine the canonical form of the expression : x 2 10 x 2 2 Justify that this expression admits as minimum value 27 and that this value is reached in 5 . E.8517 Consider the polynomial x 2 6 x +12 : 1 Determine the canonical form of this polynomial. 2 Justify that this polynomial is strictly positive for any value of x . E.4481 Consider the polynomial 6 x 2 4 x +2 . 1 Determine the canonical form of this polynomial. 2 Justify that 4 3 is the minimum value taken by this poly-nomial on R . E.8518 Consider the function f defined on R by: f ( x ) = 3 x 2 + a · x + b where a;b R Determine the values of a and b so that the function f reaches its minimum value 2 for x =3 . 5. Canonical form and direction of variations E.7252 Consider the function f defined on R by the relation: f ( x ) = x 2 + 6 x + 2 1 Justify that the function f has the canonical form : f ( x ) = x + 3 2 7 2 Establish the decrease of the function f on the interval −∞ ; 3 . Reminders: we will use the following two properties : Since the square function is decreasing on R , we have : a<b< 0 = a 2 >b 2 which translates to the sentence : ˇ two negative num-bers and their squares are compared in reverse order. ı The square function is increasing on R + , we have : 0 <a<b = a 2 <b 2 which translates to the sentence : ˇ two positive numbers and their squares are compared in the same order. ı E.7253 Consider the function f defined on R by the relation: f ( x ) = 2 x 2 + 6 x + 1 1 Show that the function f admits as canonical form : f ( x ) = 2 · x 3 2 2 + 11 2 2 Establish the decay of the function f on the interval 3 2 ; + . E.8519 Consider the function f defined by: f ( x ) = 1 x 2 + 2 x + 4 1 Establish that the defining set of f is : D f = R \ 1 5 ; 1+ 5 2 On the interval 1+ 5 ; + , establish the direction of the function f . 6. Unclassified financial years E.2296 We define the function f on R whose image of x R is defined by the relation: f ( x ) = 8 x 2 2 x + 1 1 Give the canonical form of the function f . 2 Establish that the function f is minorized by 7 8 . 3 a Establish, without justification, the table of varia-tions of the function f . https://chingmath.fr chapExoCorrec/4409 sacados/4409 chapExoCorrec/4407 sacados/4407 chapExoCorrec/8516 sacados/8516 chapExoCorrec/8517 sacados/8517 chapExoCorrec/4481 sacados/4481 chapExoCorrec/8518 sacados/8518 chapExoCorrec/7252 sacados/7252 chapExoCorrec/7253 sacados/7253 chapExoCorrec/8519 sacados/8519 chapExoCorrec/2296 sacados/2296
-2-123I-12345JOABC b Deduce that the function f admits no zero at R . E.205 Consider the function f whose image of x is defined by the relation: f ( x ) = a · x 2 + b · x + c where a , b and c are fixed real numbers, but unknown at present. Consider the representa-tion of the function f in the orthogonal frame ( O ; I ; J ) below : 1 Show that the numbers a , b , c must verify the following equation system : a b + c = 9 2 a + b + c = 1 2 4 a + 2 b + c = 3 2 Solve the previous system and derive the expression of f ( x ) . E.4568 Consider the two functions f whose im-age of a number x is given by the relation: f ( x ) = 3 · x 2 + 3 · x + 6 1 Consider the polynomial 3 · x 2 +3 · x +6 of the second de-gree: a Using the calculator, determine the two roots of this polynomial. b Draw up the sign table for this polynomial. c Deduce the definition set of the function f . 2 Using the calculator, draw up the table of variations of the function f . E.5711 1 Establish that the polynomial 2 x 2 3 x 2 admits as fac-torized form : 2 x 2 3 x 2 = 2 · x + a b · x + c where the values of the numbers a , b , c are to be specified. 2 Establish that the polynomial 12 x 2 12 x +3 admits as its factorized form : 12 x 2 12 x + 3 = 3 · 2 · x + a c · x + d where the values of the numbers a , b , c are to be specified. https://chingmath.fr chapExoCorrec/205 sacados/205 -2-123I-12345JOABC chapExoCorrec/4568 sacados/4568 chapExoCorrec/5711 sacados/5711