Outside the high school program / Second-degree function: study with the canonical form 38 exercises (including 30 corrected)

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−∞b2axa·x2b·xca>0−∞b2axa·x2b·xca<0 x-5-4-3-2-1012y-2-11234 1. Calculator and second degree E.4641 1 Consider the polynomial x 3 + x 2 3 x 3 whose repre-sentation is given opposite : a The calculator displays an integer root of this polyno-mial. Deduce a factorization of this polynomial of the form : x 3 + x 2 3 x 3 = x ¸ ˛ · x 2 + · x + b Factor this polynomial into a product of first-degree factors. 2 Following the reasoning in the previous question, factor the following polynomials into first-degree factors : a 2 x 3 2 x 2 x + 1 b x 3 + 2 x 2 2 x 4 c 2 x 3 + 3 x 2 4 x + 1 f x 3 4 x 2 3 x + 2 g 2 x 3 2 x 2 + 3 x + 1 h x 3 + 3 x 2 2 2. Second degree: variation E.4468 Reminders : A polynomial of the second degree admits as its reduced developed form a · x 2 + b · x + c where a =0 . The function x ↦− a · x 2 + b · x + c has its table of variations de-pending on the sign of the coefficient of the second-degree term : Its representative curve is called a parabola and its vertex has abscissa b 2 a . Draw up the table of variations for each of the following poly-nomials : a 4 x 2 + 4 x + 5 b 2 x 2 2 x + 3 c 2 x 2 + 4 x + 2 d 4 x 2 + 4 x + 3 e 2 x 2 + 3 x + 1 f 4 x 2 4 x 1 E.4501 1 Draw up the table of variations of the following func-tions : a f ( x ) = x 2 + x 2 b g ( x ) = 2 x 2 + 4 x 3 c h ( x ) = 4 x 2 + x + 2 d j ( x ) = 2 x 2 + 2 x + 2 2 For each function from the previous question, give, with-out specifying their values, the number of antecedents of 0 . E.4976 For each function, determine the characteristics of their extrema and draw up the table of vari-ations : a f : x ↦− 2 x 2 + 8 x + 1 b g : x ↦− x 2 + 2 x + 1 c h : x ↦− x 2 + 4 x + 4 d j : x ↦− 3 x 2 + 9 x 2 e k : x ↦− 3 x 2 + 2 x + 2 f : x ↦− x 2 + 2 3 x 1 3. Graphical representation E.8207 Consider the quadratic function f defined on R by the relation: f ( x ) = 0.4 x 2 + 0.8 x 1.2 Consider the plane equipped with the coordinate system shown below : https://chingmath.fr sacados/4641 chapExoCorrec/4468 sacados/4468 −∞b2axa·x2b·xca>0−∞b2axa·x2b·xca<0 chapExoCorrec/4501 sacados/4501 chapExoCorrec/4976 sacados/4976 chapExoCorrec/8207 sacados/8207 x-5-4-3-2-1012y-2-11234
x-2-101234y-2-112 -5-4-3-2-1I-3-2-123456JO Let C f be the curve representing the function f in the coor-dinate system above. 1 a Using a calculator, complete the tables of values be-low by entering the values of the images rounded to the nearest tenth : x 4.5 4 3 2 1.5 1 0.5 1 2 f ( x ) b Plot the representation of the curve C f . 2 Using a graph : a Draw up a table of variations for the function f . b Give the nature of the extremum of the function f and its characteristics. E.8208 Consider the quadratic function f defined on R by the relation: f ( x ) = 0.5 x 2 + x + 1.5 Consider the plane equipped with the coordinate system shown below : Let C f be the curve representing the function f in the coor-dinate system above. 1 a Using a calculator, complete the tables of values be-low by entering the values of the images rounded to the nearest tenth : x 2 1.5 1 0 0.5 1 1.5 2 3 f ( x ) b Plot the representation of the curve C f . 2 Using a graph : a Draw up a table of variations for the function f . b Give the nature of the extremum of the function f and its characteristics. E.1762 Consider the function : f : x ↦− x 2 + 4 x +1 : 1 Establish equality: f ( x )=( x +2) 2 3 2 a Determine the direction of variation of the function f on the interval −∞ ; 2 b Draw up, without justification, its table of variation. c Give the characteristics of the extremum of the func-tion f . 3 a Complete the table below of values for the function f : x 5 4 3.5 3 2.5 2 f ( x ) x 1.5 1 0.5 0 1 f ( x ) b Draw the representative curve C f of the function f in the frame below : 4. Extrema E.8204 Consider the second-degree function f defined on R by: f ( x ) = 2 x 2 8 x + 5 1 Establish identity: f ( x )=2( x 2) 2 3 2 Justify that the function f admits for minimum the value 3 reached for x =2 . E.8205 Consider the second-degree function f defined on R by: f ( x ) = 3 x 2 12 x 13 1 Establish identity: f ( x )= 3( x +2) 2 1 2 Justify that the function f admits for maximum the value 1 reached for x = 2 . https://chingmath.fr chapExoCorrec/8208 sacados/8208 x-2-101234y-2-112 chapExoCorrec/1762 sacados/1762 -5-4-3-2-1I-3-2-123456JO chapExoCorrec/8204 sacados/8204 chapExoCorrec/8205 sacados/8205
E.425 Consider the function f defined by: f : x ↦− 9 x 2 6 x 2 1 a Give the definition set of the function f . b Calculate the image of 1 by the function f . c Determine the antecedents of 2 by the function f . 2 a Establish equality: 9 x 2 6 x 2=9 x 1 3 2 3 . b Show that f admits a minimum and that this is reached in 1 3 . E.8206 For each of the second-degree func-tions below, give the nature of its extremum and its charac-teristics : 1 f ( x ) = x 2 + 4 x + 1 2 g ( x ) = 3 x 2 + 6 x 3 3 h ( x ) = x 2 + 5 x 4 4 j ( x ) = 5 x 2 + 4 x + 1 5. Sense of variation E.414 Consider the function f defined on R whose image of a number x is defined by: f ( x ) = 9 x 2 12 x + 1 1 Establish equality: f ( x )= 9 x + 2 3 2 +5 . 2 Demonstrate that, on −∞ ; 2 3 , the function f is in-creasing. E.1760 Consider the function f whose image of a real number x is defined by the relation: f ( x ) = 2 x 2 + 4 x 1 1 Establish equality: f ( x )=2( x +1) 2 3 2 Show that : a f is strictly decreasing on −∞ ; 1 . b f is strictly increasing on 1;+ . 3 Draw up the table of variations of the function f . 4 Deduce that 3 is the minimum of the function f . E.1753 Consider the function f defined on R such that the image of a number x is given by the relation: f ( x ) = 2 x 2 8 x + 9 . 1 a Establish equality: f ( x )= 2 · ( x +2) 2 +17 . b Establish the direction of variation of the function f on the interval −∞ ; 2 . 2 Draw up, without justification, the table of variations of the function f . 3 Give the characteristics of the extremum of the function f . 6. Algebraic studies E.406 Consider the function f defined on R by: f : x ↦− 2 x 2 + 2 x + 12 1 Establish the following equalities: 2 x 2 + 2 x + 12 = (3 x )(2 x + 4) = 2 x 1 2 2 + 25 2 2 a Justify that the function f cancels for two numbers to be specified. b Justify that the function f admits 25 2 as its maximum. 3 a Establish that the function f is increasing on the interval −∞ ; 1 2 . b Draw up, without justification, the table of variations of the function f on R . E.1757 Consider the function f defined on R whose image of a number x is defined by the relation: f ( x ) = 8 x 2 8 x 6 . 1 a Establish identity: f ( x ) = 4 x 6 2 x + 1 b Draw up the sign table for the function f . 2 a Establish the identity: f ( x )=8 x 1 2 2 8 . b Algebraically, establish the following inequality for any real number x : f ( x ) 8 . c On the interval −∞ ; 1 2 , establish the direction of variation of f 3 a Draw up, without justification, a table of variations of the function f . b Give, without justification, the characteristics of the extremum of the function f . 7. Table of variations and image of intervals https://chingmath.fr chapExoCorrec/425 sacados/425 chapExoCorrec/8206 sacados/8206 chapExoCorrec/414 sacados/414 chapExoCorrec/1760 sacados/1760 chapExoCorrec/1753 sacados/1753 chapExoCorrec/406 sacados/406 chapExoCorrec/1757 sacados/1757
-4-3-2-12I-2-12JOCf E.8209 1 Consider the function f defined on R by: f ( x ) = 2 x 2 x + 1 a Draw up the table of variations of the function f . b Deduce the images of the following intervals by the function f : A = 3 ; 1 4 ; B = 1 ; 2 ; C = 3 ; 1 2 Consider the function g defined on R by: g ( x ) = x 2 + 2 x 4 a Draw up the table of variations of the function g . b Deduce the images of the following intervals by the function g : D = 3 ; 0 ; E = 1 ; 3 ; G = 0 ; 3 E.405 Consider the function f defined by the relation: f ( x ) = 4 x 2 16 x + 9 . 1 Establish equality: 4 x 2 16 x +9=4( x 2) 2 7 2 Show that : a function f is decreasing on −∞ ; 2 . b function f is increasing on 2 ; + . 3 Draw up the table of variations of the function f . 4 Determine the image of the following intervals by the function f : a 2 ; 1 b 0 ; 4 c 1 ; + 8. Graphic and algebraic study E.437 Consider the function f , which to any number x , associates its image f ( x ) defined by: f ( x ) = 1 2 x 2 + x 3 2 The graph below shows the representation of the C f curve in the O ; I ; J orthonormal coordinate system : Part A : graphical study Graphically, answer the following questions : 1 Give the antecedents of the number 0 by f . 2 Draw up the table of variations of the function f on the interval 4 ; 2 . 3 Give the characteristics of the extremum of the function f . Part B: algebraic study 1 a Establish the following equality: f ( x )= 1 2 · x + 3 x 1 b Solve the equation : f ( x )=0 . 2 a Establish the following equality: f ( x )= 1 2 · x + 1 2 2 b Demonstrate that the function f is decreasing on the interval −∞ ; 1 . E.4869 Consider the function f defined by the expression : f ( x ) = a · x 2 + b · x + c where a , b , c are real numbers. The parabola C f representative of the function f has as its vertex the point with coordinates ( 1 ; 2) and passes through the point with coordinates ( 3 ; 0) . Determine, without justification, the values of the real num-bers a , b and c . https://chingmath.fr chapExoCorrec/8209 sacados/8209 chapExoCorrec/405 sacados/405 chapExoCorrec/437 sacados/437 -4-3-2-12I-2-12JOCf chapExoCorrec/4869 sacados/4869
-2-123I-4-22JO ABCDE2my3mx 3yxABCD E.6689 The curve opposite is the representation of a function f defined on 2 ; 3 . 1 Graphically, answer the following questions : a What are the images of 0 and 2 by f ? b Give, if possible : any history of 4 by f ; possible history of 4 by f ; c What are the solutions to the equation : f ( x )= 7 4 ? d What are the solutions to the inequation : f ( x ) < 0 ? 2 We admit that the function f is defined on R and admits for expression : f ( x ) = x 2 + x + 2 . a Justify that : f ( x )=( x +2)( x +1) b Solve the equation : f ( x )=0 c Using a sign table, solve the inequation f ( x ) 0 . d Justify that : f ( x )= x 1 2 2 + 9 4 . Deduce the growth of f on the interval 2 ; 1 2 . 9. Problems E.4878 Consider the figure below : It verifies the following conditions : The triangle ABC is rectangular at A such that : AB = 3 m ; AC = 2 cm The point D is defined by: D [ AB ) ; D ∈ [ AB ] point E is defined by: E [ AC ) ; E ∈ [ AC ] We have the relationship : BD + CE =10 m . Let x and y be the respective lengths of segments [ BD ] and [ CE ] . 1 a Establish the identity: 2 x 2 18 x + 153 = 2 x 9 2 2 + 225 2 b Determine the values of x and y so that the length of the segment [ DE ] is minimal. 2 Determine the possible values of x and y so that the area of the hatched part measures 15 m 2 10. Modeling E.2865 We want to construct a rectangular play area along the side of a building. Furthermore, we want the dimensions of this rectangle to be greater than or equal to 10 m . This playing area is surrounded on three sides by a 3 m wide alley as shown in the sketch below. The set is fenced on three sides [ AB ] , [ BC ] and [ CD ] . We are interested in the length L of the fence : L = AB + BC + CD . Let x and y be the dimensions in meters of the playing area (the value of x and y are necessarily positive) . 1 Express the length L of the fence in terms of the values of x and y . 2 We have 100 meters of fence that we want to use entirely: a Express, under these conditions, the value of y as a function of x . b Justify that the value of x must be less than 44. c Justify that the area of the playground is : A ( x ) = 88 x 2 x 2 3 a Justify the equality below : A ( x ) = 968 2( x 22) 2 https://chingmath.fr chapExoCorrec/6689 sacados/6689 -2-123I-4-22JO chapExoCorrec/4878 sacados/4878 fichierPlus/4878/ ABCDE2my3mx chapExoCorrec/2865 sacados/2865 3yxABCD
xcmycm3cm b Deduce the growth of the function A on the interval 0 ; 22 . c Draw up, without justification, the table of variations of the function A on the interval 0 ; 44 . 4 Deduce the dimensions so that the 100 meters of fencing are used and the play area is maximized. E.2877 A carpenter has a stick of wood 100 centimetres long and 3 centimetres wide. He wants to use the full length of this stick to make a wooden frame like the one shown in the drawing below : 1 a Determine the value of y as a function of x . b Deduce the possible values of x . 2 Give the expression for the area A ( x ) of the inside of the frame as a function of x . 3 a Establish the following equality: A ( x ) = ( x 28) 2 + 484 b Establish the growth of the function A on the interval 6 ; 28 . c Draw up the table of variations of the function A , then give the maximum area reached by the frame. E.3024 At a funfair, the manager of the attraction ˇ the crazy caterpillar ı makes the following obser-vation : Its carousel can accommodate 70 people per ride ; If he sets the price at 1 e , his ride is full every round ; Every time he increases the price by 0.50 e , he loses 5 customers. Let x be the price of a seat : the number x belongs to the interval 1 ; + [ . We are interested in the value of the revenue made by this at-traction each round as a function of the price x of the seats ; we note R ( x ) the value of this revenue. 1 Justify that the recipe admits the expression : R ( x ) = 80 x 10 x 2 2 a Draw up the table of variations of the function R . b Deduce the maximum revenue this attraction can achieve. What must the price of a ride be to achieve this maximum? 3 The manager wants to earn more than 150 e à for each ride. Let’s determine the possible prices of a seat meeting this condition : a Expand the expression : ( x 4) 2 1 . Deduce the canonical form of the expression R ( x ) 150 . b Factor the expression : ( x 4) 2 1 2 . Then factor the expression R ( x ) 150 . c Determine the solutions of the equation : R ( x )=150 . d Using the previous question and the table of variations of the function R , give without justification the set of solutions of the inequation R ( x ) 150 . https://chingmath.fr chapExoCorrec/2877 sacados/2877 xcmycm3cm chapExoCorrec/3024 sacados/3024
ABCMNPQO 2345678I2345JOABS BMRO8kmij E.4852 Consider the isosceles triangle ABC of dimensions : OA = 8 cm ; OC = 5 cm [ CO ] represents the height of the triangle ABC originating from the vertex C . We wish to inscribe a rectangle MNPQ inside the triangle and centered around the axis ( OC ) as shown above. Note x the length of segment [ OP ] . 1 Briefly justify the possible values taken by the variable x . 2 Determine the measure of segment [ NP ] as a function of length x . 3 Show that the area A of the rectangle MNPQ is ex-pressed as a function of x : A ( x ) = 5 4 · x 2 + 10 · x 4 For what value is the area of the rectangle MNPQ max-imum? E.3078 A basketball player at point A shoots a free throw towards the basket at B ; the ball’s trajectory passes through a vertex named S . Joe, the mathematician sitting in the bleachers, uses a O ; I ; J orthonormal reference frame to model this trajec-tory: He notes the coordinates of the following points : A (1 ; 1) ; B (7 ; 2) ; S (4.5 ; y S ) (Joe didn’t have time to pick up the y-intercept of the S vertex) Neglecting friction in the air, Joe knows that any projectile describes a parabolic trajectory whose Cartesian equation is of the form : ( E ) : y = a · x 2 + b · x + c 1 a Using the coordinates of vertex S , justify the follow-ing equality: b = 9 a b Justify that the real numbers a and b verify the system of equations : c 8 a = 1 c 14 a = 2 c Deduce the equation ( E ) representing the curve C . 2 A second player makes his throw ; Joe obtains the equa-tion representing the second trajectory : ( E ) : y = 1 8 · x 2 + 7 6 · x 1 24 a Determine the values of a and b verifying the equality below : 3 x 2 + 28 x 49 = x 7 a · x + b b Deduce the abscissas where the ball will be at a height of 2 m . E.2988 A boat has to navigate between the shore and a rock. This rock is 8 km from the shore. For safety reasons, the captain wishes to keep an equal dis-tance from the rock and the shore. To model this problem, we’ll use the reference frame O ; i ; j whose point O is the orthogonal project of point R onto the shoreline. Note ( x ; y ) the coordinates of the boat in this frame of refer-ence. 1 Express as a function of x and y the distance separating the boat: a du rocher b du rivage 2 a Using the equality BR = BM , express the value of y as a function of x . b What is the name of the boat’s trajectory? 11. Problems and signs E.2985 In the plane, consider a rectangle ABCD such that : DC = 7 cm ; DA = 5 cm The points I , J , K , L are points belonging respectively to the sides [ AB ] , [ BC ] , [ CD ] , [ DA ] verifying the relations : DK = CJ = BI = LA = x cm https://chingmath.fr chapExoCorrec/4852 sacados/4852 ABCMNPQO chapExoCorrec/3078 sacados/3078 2345678I2345JOABS chapExoCorrec/2988 sacados/2988 BMRO8kmij chapExoCorrec/2985 sacados/2985
ABCDIJKLxcm ABMCCC 1 Justify, briefly, that the quadrilateral IJKL is a paral-lelogram. 2 a Determine the possible values for x . b Justify that the area of the parallelogram IJKL has the expression as a function of x : A ( x ) = 2 x 2 12 x + 35 c Deduce the table of variations of the function A . d Give the minimum of the value of the area of IJKL and the value of x for which it is reached. 3 We wish to determine the values of x for which, A is greater than 25 cm 2 a Determine the values of a and b real numbers verifying the equality: 2 x 2 12 x + 10 = ( a · x + b )( x 5) b Deduce the solutions of the inequation : A ( x ) 25 cm 2 . E.3003 In the plane, consider the circle C of diameter [ AB ] such that AB =5 cm . Let M be a point on the segment [ AB ] , we construct the circles C and C  of diameters [ AM ] and [ MB ] respectively. We mark the position of point M by the measure of AM , which we note x ; we are interested in the area of the hatched part, which we note A ( x ) . 1 Briefly describe the values taken by the variable x . 2 Determine an expression for A as a function of x . Consider the function that to x associates A ( x ) 3 Draw up the table of variations of the function A ( x ) . 4 a Determine the value of the reals a and b such that : 2 x 2 + 10 x 8 = ( x 4)( a · x + b ) b Solve the following inequation : A ( x ) 2 · ı 12. Calculator and polynomial E.4635 Consider the function f whose im-age of a real number x is defined by the relation: f ( x ) = 2 x 3 12 x 2 + 2 x + 12 The representation of this function is given in the screenshot opposite from a calculator. Of the following expressions, only one represents the factor-ized form of this polynomial. Which is it? a 2( x 1)( x + 1)( x 6) b 2( x 1)( x + 1)( x + 6) c 2(1 x )( x + 1)( x + 6) d 2(1 x )( x + 1)( x 6) Check your answer. E.4634 Consider the function f whose im-age of a real number x is defined by the relation: f ( x ) = x 3 + 3 x 2 6 x 8 The representation of this function is shown in the screenshot of a calculator opposite. Among the following expressions, only one represents the fac-tored form of this polynomial. Which one? a ( x + 2)( x 1)( x 4) b ( x 2)( x + 1)( x + 4) c ( x 1)( x 2)( x + 4) d ( x + 4)( x 1)( x + 2) Check your answer. https://chingmath.fr ABCDIJKLxcm chapExoCorrec/3003 sacados/3003 ABMCCC sacados/4635 sacados/4634
16cmxx10cm 1612xx 4cm6cmyxABCDEFG E.4636 1 Consider the two functions f and g defined by: f ( x ) = x 3 + x 2 + 4 x + 2 g ( x ) = x 1 Representations of these two functions are given in the screenshot opposite from a calculator. a Use your calculator to describe the set of solutions to the equation : f ( x ) = g ( x ) b For each of the two equalities below, determine the values of the real ¸ , ˛ and realizing these equalities: x 3 + x 2 + 5 x + 3 = x + 1 ¸ · x 2 + ˛ · x + x 3 + x 2 + 5 x + 3 = x 3 ¸ · x 2 + ˛ · x + c Using the previous question, affirm the conjecture in question a . 2 Consider the two functions f and g defined by: f ( x ) = 2 x 3 5 x + 6 ; g ( x ) = x + 2 Follow the approach in the previous question to deter-mine the set of solutions of the equation : f ( x ) = g ( x ) E.4633 1 Using the calculator, conjecture the factorized form of the following polynomials: a x 3 + 3 x 2 6 x 8 b x 3 3 x 2 x + 3 c x 3 x 2 + 4 x + 4 d 3 x 2 6 x 2 3 x + 6 e 4 x 3 + 8 x 2 4 x 8 f 2 x 3 + 4 x 2 + 6 x 2 Algebraically verify your conjectures from the previous question. E.4639 Solve the following inequations : a x 3 4 x 2 + x + 6 < 0 b 2 x 3 + 4 x 2 6 x 0 c 2 x 3 4 x 2 + 2 x + 4 > 0 d 2 x 3 + 2 x 2 2 x 2 0 E.4638 In the pattern below, we want to make a rectangular box without a lid. The lengths are expressed in cm . Deduce the value(s) of x for which this box has an area of 144 cm 2 . E.4637 On a former wasteland of rectangular shape of length 16 m and 12 m , the municipality wishes to build a kindergarten with a driveway running around the play area: The playground is represented below by the hatched area: Quelle (s) dimension (s) can the width of the driveway be so that the play area is the same as the driveway? 13. Unclassified financial years E.4879 Let ABCD be a rectangle with di-mensions 6 cm and 4 cm . Consider the points E and G , lo-cated outside the rectangle ABCD , belonging respectively to the half-lines [ AB ) and [ AD ) and the point F such that the quadrilateral AGFE is a rectangle. We note x and y the following two distances : x = DG ; y = BE Points E and G must form a rectangle AEFG with a perime-ter of 28 cm . 1 a Show that the length y is expressed as a function of x by: y =4 x b Deduce the possible values of x . Let A be the area of the shaded part (that of the polygon BEFGDC ) . 2 Establish that the area of the shaded region can be writ-ten as a function of x is obtained by the equation : A ( x ) = x 2 + 2 x + 24 3 Draw up the table of variations of the function A on R . (indicate the value of the local extremum) . 4 Let’s study the extreme values taken by the shaded area of this figure : a What is the maximum area of the shaded part? For https://chingmath.fr sacados/4636 sacados/4633 sacados/4639 sacados/4638 16cmxx10cm sacados/4637 1612xx chapExoCorrec/4879 sacados/4879 4cm6cmyxABCDEFG
what values of x is it reached? b What is the minimum area of the shaded part? For what value of x is this minimum achieved? https://chingmath.fr