Outside the middle school program / Geometry in space 9 exercises (including 7 corrected)

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ABCDEF6cm3;2cm6;8cm3cm ABCDEFGH ABCDEFGHIJ ABCDEFGIOIH 1. Lateral surface E.6604 Consider the right prism ABCDEF shown below : 1 a What is the nature of the face DEF ? b Determine the area of face DFE . 2 a Of what natures are the faces ABED , ACFD and BCFE ? b Determine the area of each of these faces. 3 Give the lateral area of this right prism. E.4949 Consider the cube ABCDEFGH with side 4 cm shown below : 1 a How many vertices does this cube have? b How many edges does this cube have? c How many faces does this cube have? 2 Determine the volume of this cube. 3 Determine the lateral area of this cube. E.586 Consider the right block ABCDEFGH ; note I and J the respective middles of the ABCD and EFGH faces. The following measurements are now assumed to be known : AB = 8 cm ; AD = 6 cm ; AE = 7 cm and we admit that the solid IDCJHG is a right prism : 1 Calculate the volume of the prism IDCJHG . 2 Calculate the lateral surface area of the prism IDCJHG . E.9123 The volume of the parallelepiped has been multiplied by 27. By how much have its dimensions been en-larged? And its lateral area? 2. Volume expansion and reduction E.5461 Consider a pyramid ABCDO with a square base ABCD shown opposite. Let I be the foot of the pyramid’s height and E the mid-point of [ OA ] . We have the dimensions : AB =3 cm ; IO =4 cm The plane parallel to the base passing through point E inter-sects. the pyramid, forming quadrilateral EFGH . 1 a What is the nature of the quadrilateral EFGH ? b Justify that point F is the midpoint of segment [ OB ] . c What can be said about pyramid EFGHO in relation to pyramid ABCDO ? 2 a Determine the length of segment [ EF ] . b Give the area A of the base ABCD and the area A of the vase EFGH . c Give the value of the ratio A A of the areas. 3 The formula for a pyramid is given by the formula : V = 1 3 ×A B × h It is assumed that : OI =2 cm https://chingmath.fr chapExoCorrec/6604 sacados/6604 ABCDEF6cm3;2cm6;8cm3cm chapExoCorrec/4949 sacados/4949 ABCDEFGH chapExoCorrec/586 sacados/586 ABCDEFGHIJ chapExoCorrec/9123 sacados/9123 chapExoCorrec/5461 sacados/5461 ABCDEFGIOIH
ABCDS SADCBABCDSADCBOADCBO ABCDHS ABCDHSMNOP a Give the volume V of the pyramid ABCDO and the volume V of the pyramid EFGHO . b Give the value of the ratio V V of the volumes. E.6299 Paul visiting Paris admires the Pyramid, made of laminated glass in the center of the Louvre’s inner courtyard. This regular pyramid has : base a square ABCD side 35 meters ; for height the segment [ SO ] of length 22 meters. Paul enjoyed the pyramid so much that as a souvenir of his visit he bought an oil lamp whose glass reservoir is a scale reduction 1 500 of the real pyramid. The lamp’s instructions state that, once lit, it burns 4 cm 3 of oil per hour. After how long will there be no oil left in the reservoir? Round off to the nearest hour. Reminder : Volume of a pyramid = one-third of the product of the area of the base times the height. Show the approach used on the copy. Any trace of research will be taken into account during assessment even if the work is not completely finished. E.987 An hourglass consists of two super-imposed pyramids, as shown in the sketch below. The sand flows at point S . The surface of the sand is represented by the plane A B C D horizontal and parallel to the bases of the pyramids SABCD The pyramid SABCD is regular, its base is a square ABCD , recall that the height ( SO ) is perpendicular to the plane ABCD . The sand level is marked by the length SA on the pyramid edge SABCD . We give : OA =27 mm et SO =120 mm . Throughout this problem, A is the middle of [ SA ] . 1 Represent the base ABCD in full size. 2 a Justify that the triangle AOB is isosceles rectangle. b Show that : AB =27 2 mm 3 a Calculate the area of the square ABCD b Deduce the volume V of the pyramid SABCD is 58 320 mm 2 4 The triangle SOA is right-angled. Show that : SA = 123 mm . 5 Pyramid SA B C D is a reduction of the SABCD pyra-mid. a What can we say about the straight lines ( OA ) and ( O A ) ? b Determine the coefficient of reduction SO SO . 6 Note V the volume of the pyramid SA B C D . Calculer V . 7 It is assumed that the volume of sand lowered is propor-tional to the time elapsed. all the sand runs out in 4 minutes. After how long is the sand level in the position studied? E.5920 A regular pyramid with vertex S has base ABCD square such that its volume V is equal to 108 cm 3 . Its height measures 9 cm . The volume of a pyramid is given by the relationship : Volume of a pyramide = aire of the base × hauteur 3 1 Verify that the area of ABCD is 36 cm 3 . Deduce the value of AB . Show that the perimeter of the triangle ABC is equal to 12+6 2 cm . 2 SMNOP is a reduction of the pyramid SABCD . We then obtain the pyramid SMNOP such that the area of the square MNOP is equal to 4 cm 2 a Calculate the volume of the pyramid SMNOP . b For this question, any trace of research, however incomplete, will be taken into account in the evaluation . Elise thinks that to obtain the perimeter of the triangle MNO , we simply divide the perimeter of the triangle ABC by 3 . Do you agree with her? https://chingmath.fr sacados/6299 ABCDS chapExoCorrec/987 sacados/987 Afrique de l'ouest et Asie - juin 2005 - 12 points SADCBABCDSADCBOADCBO sacados/5920 ABCDHS ABCDHSMNOP
SABCDEFGH SABCDMNPQ 3. Pyramid, enlargement, reduction, affine functions E.991 In the figure opposite, SABCD is a square-based pyramid of height [ SA ] such that : AB =9 cm ; SA =12 cm . The triangle SAB is right-angled at A . First part EFGH is the section of the pyramid SABCD by the plane parallel to the base and such that : SE =3 cm . 1 a Calculate EF . b Calculate SB . 2 a Calculate the volume V of the pyramid SABCD . b Give the reduction coefficient to go from pyramid SABCD to pyramid SEFGH . c Deduce the volume V of SEFGH . A value rounded to unity will be given. Second part Let M be a point of [ SA ] such that SM = x cm , where x is between 0 and 12. We call MNPQ the section of the pyramid SABCD by the plane parallel to the base passing through M . 1 Show that : MN =0.75 · x 2 Let A ( x ) be the area of the square MNPQ as a function of x . Show that : A ( x )=0.5625 · x 2 . 3 Complete the table below : Longueur x (en cm ) 0 2 4 6 8 10 12 Area A ( x ) of the square MNPQ 4 Draw a reference frame where : on the x-axis, 1 cm represents 1 unit ; on the ordinate axis, 1 cm represents 10 units. the x-axis and y-axis are perpendicular. Place in this frame the points with abscissa x and ordi-nate A ( x ) given by the table. 5 Is the area of MNPQ proportional to the length SM ? Justify using the graph. https://chingmath.fr chapExoCorrec/991 sacados/991 Paris - Juin 2006 - 12 points SABCDEFGH SABCDMNPQ