Outside the high school program / Surfaces 18 exercises (including 16 corrected)

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ABCDEFGHijk y-6-4-2A2468z-4-22468101214jk 1. Usual surface area E.4120 In space, consider the ABCDEFGH cube shown below with center O . The plane is given the orthonormal reference frame C ; CB ; CD ; CG Determine the equations of the following planes : a ( BCD ) b ( GHD ) c ( FEH ) d ( ABF ) e ( ABG ) f ( BDG ) E.4121 The space is given a reference frame O ; i ; j ; k . Determine the Cartesian equations of the following surfaces : 1 The cylinder of axis O ; j passing through the point A 0 ; 0 ; 3 . 2 The cylinder of axis O ; k passing through the point B 3 ; 3 ; 0 . 3 The cone with vertex O and axis of revolution O ; i passing through the point C 3 ; 2 ; 2 . 4 The cylinder of axis O ; i and whose section with the plane of equation x = 3 is a circle of radius 4 . 5 The cone with vertex O and axis of revolution O ; k whose section with the plane of equation z =2 is a circle of radius 2 . 2. Intersection of a surface and a plane E.4098 Space is provided with an or-thonormal reference frame O ; i ; j . Consider the surfaces S 1 and S 2 of respective equations : z = x 2 + y 2 ; z = x · y + 2 x Note P the plane of equation x =2 , E 1 the intersection of surface S 1 and plane P and E 2 the intersection of surface S 2 and plane P . In appendix , the P plane is represented fitted with the A ; j ; k where A is the point with coordinates 2 ; 0 ; 0 . 1 a Determine the nature of the set E 1 . b Determine the nature of the set E 2 . 2 a Represent the sets E 1 and E 2 on the attached sheet. b In the reference frame O ; i ; j ; k give the coordi-nates of the intersection points B and C of the sets E 1 and E 2 . https://chingmath.fr chapExoCorrec/4120 sacados/4120 ABCDEFGHijk chapExoCorrec/4121 sacados/4121 chapExoCorrec/4098 sacados/4098 Extrait d'Antilles-Guyane Septembre 2009 y-6-4-2A2468z-4-22468101214jk
Figure no1Figure no2Figure no3Figure no4 Oijk E.4114 In the space equipped with an orthonormal reference frame O ; i ; j ; k , we consider the points : A 1 ; 3 ; 2 ; B 4 ; 6 ; 4 and the cone (Γ) with axis O ; k , with vertex O and con-taining the point A . 1 Show that an equation of (Γ) is : x 2 + y 2 = 5 2 · z 2 2 Let ( P ) be the plane parallel to the plane ( xOy ) and containing the point B . a Determine an equation of ( P ) . b Specify the nature of the intersection ( C 1 ) of ( P ) and (Γ) . E.4117 In space provided with the orthonormal reference frame O ; i ; j ; k , note S the surface of equa-tion : z = x 2 + 2 · x + y 2 + 1 Say if, yes or no, ˇ the section of S with the plane of equa-tion z =5 is a circle of center A of coordinates 1 ; 0 ; 5 and radius 5 ı. E.4138 Space is provided with an or-thonormal reference frame O ; i ; j ; k . Surface study S equation z = 1 4 · x · y 1 We cut S through the plane ( xOy ) . Determine the sec-tion obtained. 2 We cut S by a plane P parallel to the plane ( xOy ) . What is the nature of the section obtained? 3 In this question, any trace of research, however incom-plete, or initiative, however unsuccessful, will be taken into account in the assessment. We cut S by the plane with equation x + y =0 . What is the nature of the resulting cross-section? E.4135 In the reference frame O ; i ; j ; k , S is the surface of equation : 4 · z = x · y . The following figures show the intersections of S with certain planes of space. 1 S 1 denotes the section of the surface S through the plane ( xOy ) . One of the figures given represents S 1 which one? 2 S 2 designates the section of S by the plane R of equation z =1 . One of the given figures represents S 2 , which one? 3 S 3 denotes the section of S through the plane of equation y =8 . One of the figures given represents S 3 , which one? E.4136 For each of the following questions, indicate whether the proposed statement is true or false and justify the answer. Space is provided with an orthonormal reference frame O ; i ; j ; k . 1 E is the set of points M space whose coordinates ( x ; y ; z ) verify the equation : z = x 2 + y 2 . Note S the section of E by the plane of equation y = 3 . Assertion: S is a circle. 2 P is the surface of equation x 2 + y 2 =3 · z 2 Assertion: O is the only point of intersection of P with the plane ( yOz ) with integer coordinates. E.4311 Space is provided with an orthonor-mal reference frame O ; i ; j ; k . Consider the surface S , one equation of which is : z = 4 · x · y Show that the section of the surface S through the plane of equation z =0 is the union of two orthogonal straight lines. 3. Volume E.4140 For each of the following two propositions, indicate whether it is true or false and give a demonstration of the chosen answer. An unproven answer scores no points. Space is referred to an orthonormal refer-ence frame O ; i ; j ; k . The surface Σ opposite has the equation : z = x 2 + y 2 1 The section of the surface Σ and the plane of equation x = , where is a real, is a hyperbola. 2 The plane of equation z = 9 · 2 2 di-vides the solid bounded by Σ and the plane of equation z =9 into two solids of equal volume. Reminder. Let V be the volume of the solid bounded by Σ https://chingmath.fr chapExoCorrec/4114 sacados/4114 chapExoCorrec/4117 sacados/4117 chapExoCorrec/4138 sacados/4138 Extrait d'Ameriques du Sud Novembre 2008 chapExoCorrec/4135 sacados/4135 Extrait Centres Etrangers Juin 2009 Figure no1Figure no2Figure no3Figure no4 chapExoCorrec/4136 sacados/4136 Extrait d'Antilles-Guyanes Juin 2009 sacados/4311 chapExoCorrec/4140 sacados/4140 Extrait de Liban Mai 2008 Oijk
Figure no1Figure no2Figure no3 and the planes of equations z = a and z = b where 0 a b 9 . V is given by the formula V = b a S ( k ) d k where S ( k ) is the cross-sectional area of the solid through the plane of equation z = k where k a ; b . 4. Annales - Study of surfaces E.4143 The space ( E ) is equipped with an orthonormal basis O ; i ; j ; k . Consider the points : A 0 ; 5 ; 5 ; B 0 ; 0 ; 10 1 In this question, we are working in the plane P 0 with equation x = 0 relative to the coordinate system O ; i ; j . Let C be the circle with center B and passing through A . Prove that the line ( OA ) is tangent to the circle C . 2 We call S the sphere generated by the rotation of the circle C around the axis ( Oz ) and Γ the cone generated by the rotation of the line ( OA ) around the axis ( Oz ) . a Prove that the cone Γ has the equation : x 2 + y 2 = z 2 b Determine the intersection of the cone Γ and the sphere S . Specify the nature of this intersection and its charac- teristic elements. c Illustrate these objects with a diagram in space. 3 We cut the cone Γ by the plane P 1 with equation x =1 . In P 1 , one of the three figures below represents this in-tersection. Identify this figure and provide the necessary justifica-tion. 4 Let M ( x ; y ; z ) be a point on the cone Γ whose coordi-nates are non-zero relative integers. Prove that x and y cannot both be odd. 5. Annales - Surfaces and arithmetic E.4087 Part A Consider, in a coordinate system O ; i ; j ; k in space, the surface S with equation : z = x y ) 2 1 We denote E 1 the intersection of S with the plane P 1 of equation z =0 . Determine the nature of E 1 . 2 We note E 2 the intersection of S with the plane P 2 of equation x =1 . Determine the nature of E 2 . Part B Consider, in a coordinate system O ; i ; j ; k in space, the surface S with equation : z = x · y 1 We note E 3 the intersection of S with the plane P 1 of equation z =0 . Determine the nature of E 3 . 2 We note E 4 the intersection of S with the plane P 3 of equation z =1 . Determine the nature of E 4 . Part C Let E 5 be the intersection of S and S . In this section, we want to show that the only point belong-ing to E 5 whose coordinates are natural numbers is the point O 0 ; 0 ; 0 . We assume that there is a point M belonging to E 5 and whose coordinates x , y and z are natural integers. 1 Show that if x =0 , then the point M is the point O 2 We now assume that the integer x , y and z vérifient : x 2 3 · x · y + y 2 = 0 . Deduce that there then exist natural numbers x and y premiers between them such that : x 2 3 · x · y + y 2 = 0 3 Show that x divides y 2 , then, that x divise y . 4 Establish that y verify the relationship : 1 3 · y + y 2 = 0 5 Conclude. https://chingmath.fr chapExoCorrec/4143 sacados/4143 Pondichery Avril 2004 Figure no1Figure no2Figure no3 chapExoCorrec/4087 sacados/4087 Pondichery Avril 2011 5 points
E.4132 The space is equipped with an orthonor-mal basis O ; i ; j ; j . We consider the surface S 1 of equation z = x 2 + y 2 and the surface S 2 of equation z = x · y +2 · x Part A Let P be the plane of equation x =2 , E 1 the intersection of the surface S 1 and the plane P and E 2 the intersection of the surface S 2 and the plane P . In the appendix, the plane P is marked with the reference A ; i ; j where A is the point with coordinates 2 ; 0 ; 0 . 1 a Determine the nature of the set E 1 . b Determine the nature of the set E 2 . 2 a Represent the sets E 1 and E 2 on the sheet ap-pendix . b In the reference point O ; i ; j ; k give the coordi-nates of the points of intersection B and C of the sets E 1 and E 2 . Part B The following property can be used without proof : ˇLet a , b and c be integers with a prime. If a divides b · c then a divides b or a divides c . ı The objective of this section is to determine the points of in-tersection M ( x ; y ; z ) of the surfaces S 1 and S 2 where y and z are relative integers and x is a prime integer. We consider such a point M ( x ; y ; z ) . 1 a Show that : y ( y x )= x (2 x ) . b Deduce that the prime number x divides y . 2 We set y = k · x with k Z . a Show that x divides 2 , then that x =2 . b Deduce the possible values of k . 3 Determine the possible coordinates of M and compare the results with those in part A question 2 b . E.4137 The space is equipped with an orthonormal basis O ; i ; j ; k . 1 Let F be the point with coordinates 0 ; 0 ; 1 4 and P be the plane with equation z = 1 4 . Let d ( M;P ) be the distance from a point M to the plane P . Show that the set ( S ) of points M with coordinates ( x ; y ; z ) that satisfy d ( M ; P )= MF a has the equation : x 2 + y 2 = z . 2 a What is the nature of the intersection of the set ( S ) with the plane of equation z =2 ? b What is the nature of the intersection of the set ( S ) with the plane of equation x =0 ? Represent this intersection in the coordinate system O ; j ; k 3 In this question, x and y denote natural numbers. a What are the possible remainders of the Euclidean di-vision of x 2 by 7 ? b Prove that 7 divides x 2 + y 2 if, and only if, 7 divides x and 7 divides y . 4 In this question, any attempt at research, even if incom-plete, or any initiative, even if unsuccessful, will be taken into account in the assessment. Are there any points that belong to the intersection of the set ( S ) and the plane of equation z = 98 and whose coordinates are all natural numbers? If so, determine them. https://chingmath.fr chapExoCorrec/4132 sacados/4132 chapExoCorrec/4137 sacados/4137 La R&union Juin 2009
E.4141 In the space equipped with an orthonormal reference frame O ; i ; j ; j , we consider the points A 1 ; 3 ; 2 and B 4 ; 6 ; 4 and the cone (Γ) with axis O ; k , with vertex O and containing the point A . Part A 1 Show that an equation of (Γ) is : x 2 + y 2 = 5 2 · z 2 2 Let ( P ) be the plane parallel to the plane ( xOy ) and containing the point B , a Determine an equation of ( P ) . b Specify the nature of the intersection ( C 1 ) of ( P ) and (Γ) . 3 Let ( Q ) be the equation plane y =3 . We note ( C 2 ) the intersection of (Γ) and ( Q ) . Without justification, iden-tify the nature of ( C 2 ) from among the following propo-sitions : a two parallel lines ; b two intersecting lines ; c a parabola; d a hyperbola; e a circle. Part B Let x , y and z be three relative integers and M the point with coordinates ( x ; y ; z ) . The sets ( C 1 ) and ( C 2 ) are the sections defined in part A . 1 Consider the equation ( E ): x 2 + y 2 =40 where x and y are relative integers. a Solve the equation ( E ) . b Deduce all points of ( C 1 ) whose coordinates are rela-tive integers. 2 a Prove that if the point M with coordinates ( x ; y ; z ) where x , y and z denote relative integers, is a point of (Γ) then z is divisible by 2 and x 2 + y 2 is divisible by 10 . b Show that if M is a point of ( C 2 ) , intersection of (Γ) and ( Q ) , then : x 2 1 ( mod. 10) c Determine a point ( C 2 ) , distinct from A , whose coor-dinates are relative integers. E.4139 The space is referenced to the orthonormal coordinate system O ; i ; j ; k . We call ( S ) the surface with equation : x 2 + y 2 z 2 = 1 1 Show that the surface ( S ) is symmetrical with respect to the plane xOy . 2 We call A and B the points with the respective coordi-nates : 3 ; 1 ; 3 ; 1 ; 1 ; 1 a Determine a parametric representation of the line ( D ) passing through the points A and B . b Prove that the line ( D ) is included in the surface ( S ) . 3 Determine the nature of the section of the surface ( S ) by a plane parallel to the plane ( xOy ) . 4 a Consider the curve ( C ) , the intersection of the sur-face ( S ) and the plane with equation z = 68 . Specify the characteristic elements of this curve. b M being a point of ( C ) , we designate a as its abscissa and b as its ordinate. We propose to show that there is only one point M of ( C ) such that a and b are natural integers satisfying : a <b ; ppcm ( a ; b ) = 440 . That is, such that ( a ; b ) is a solution to the system : (1) : a <b a 2 + b 2 = 4625 ppcm ( a ; b ) = 440 Show that if ( a ; b ) is a solution of (1) then pgcd ( a ; b ) is equal to 1 or to 5 . Conclude. In this question any trace of research, even if incom-plete, or initiative, even if unsuccessful, will be taken into account in the assessment. 6. Annales - Volume E.4199 The space ( E ) is equipped with an orthonormal basis O ; i ; j . We consider the surface T with equation : x 2 · y = z with 1 x 1 and 1 y 1 . The figure opposite is a representation of the surface T in the cube with center O and side length 2 . 1 Elements of symmetry of the surface T . a Show that if point M ( x ; y ; z ) belongs to T , then point M ( x ; y ; z ) also belongs to T . Deduce a plane of symmetry of T . b Show that the origin O of the coordinate system is the center of symmetry of T . 2 Intersections of the surface T with planes parallel to the axes. a Determine the nature of the intersection curves of T with planes parallel to the plane ( xOz ) . b Determine the nature of the intersection curves of T with planes parallel to the plane ( yOz ) . 3 Intersections of the surface T with planes parallel to the plane ( xOy ) of equations z = k , avec k 0 ; 1 . a Determine the intersection of the surface T and the plane of equation z =0 . b For k> 0 , we note K the point with coordinates 0 ; 0 ; k . Determine, in the coordinate system K ; i ; j , the equation of the intersection curve of T and the plane with equation z = k . c Draw the shape of this curve in the coordinate system K ; i ; j . Specify in particular the coordinates of the endpoints of the arc. https://chingmath.fr chapExoCorrec/4141 sacados/4141 Polynesie Juin 2007 chapExoCorrec/4139 sacados/4139 Ameriques du Nord Mai 2008 chapExoCorrec/4199 sacados/4199
4 We denote ( D ) the domain formed by the points of the unit cube located below the surface T : ( D )= M ( x ; y ; z ) ( E ) 0 x 1 ; 0 y 1 ; 0 z x 2 · y a For 0 <k 1 , the plane of equation z = k coupe the do-main ( D ) selon a surface that can be visualized on the graph in question 3 c . This is the set of points M of the unit cube with coor-dinates ( x ; y ; z ) such as : y k x 2 et z = k . Calculate as a function of k the area S ( k ) expressed in units of area of this surface. b We pose S (0)=1 ; calculate in units of volume, the volume V du domain ( D ) . Recall that : V = 1 0 S ( k ) dk . E.4319 Part A : Organized knowledge retrieval 1 Prerequisite : any integer n strictly greater than 1 has at least one prime divisor. Prove that every integer n strictly greater than 1 is prime or can be decomposed into a product of prime factors (we do not ask you to prove the uniqueness of this decompo-sition) . 2 Give the decomposition into prime factors of 629 . Part B In an orthonormal coordinate system O ; i ; j ; k , we consider the surfaces Γ and C with respective equations : Γ : z = x · y ; C : x 2 + z 2 = 1 1 Give the nature of the surface C and determine its char-acteristic elements. 2 Points of intersection with integer coordinates of surfaces Γ and C . a Show that the coordinates ( x ; y ; z ) of the intersection points of Γ and C are such that : x 2 · 1 + y 2 = 1 b Deduce that Γ and C have two points of intersection whose coordinates are relative integers. 3 Points of intersection with integer coordinates of Γ and a plane. For any non-zero natural number n , we denote by P n the plane of equation z = n 4 +4 a Determine the set of intersection points of Γ and the plane P 1 whose coordinates are relative integers. for the rest of the exercise, we assume n 2 . b Check that : n 2 2 · n + 2 n 2 + 2 · n + 2 = n 4 + 4 c Prove that, regardless of the natural number n 2 , the integer n 4 +4 is not prime. d Deduce that the number of points of intersection of Γ and the plane P n whose coordinates are relative inte-gers is greater than or equal to 8 . e Determine the points of intersection of Γ and the plane P 5 whose coordinates are relative integers. https://chingmath.fr sacados/4319 Asie Juin 2011 5 points