(a) Write down and OB in terms of the unit vectors i, j and k. (b) Calculate OA OB and hence calculate the angle AOB. (c) Calculate OAX OB and hence calculate the ratio of the surface area of the octahedron to the surface area of the cube.

Elementary Geometry For College Students, 7e
7th Edition
ISBN:9781337614085
Author:Alexander, Daniel C.; Koeberlein, Geralyn M.
Publisher:Alexander, Daniel C.; Koeberlein, Geralyn M.
Chapter9: Surfaces And Solids
Section9.2: Pyramids, Area, And Volume
Problem 6E
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For every polyhedron there is a construction for a so called dual
polyhedron by connecting together the centres of the faces. The
diagram on the left below shows this construction for a cube that
constructs an octahedron inside it.
V₂.
B
A
i
0
Choose an origin O to be the centre of the base of the cube and choose
the i, j and k directions to be parallel to the faces of the cube. Let A be
the centre of the face with positive i-coordinate and B be the centre of
the face with positive j- coordinate, as shown in the right-hand diagram.
Let the cube have a side length 2.
(a) Write down OA and OB in terms of the unit vectors i, j and k.
(b) Calculate OA OB and hence calculate the angle AOB.
(c) Calculate OÀ X OB and hence calculate the ratio of the surface
area of the octahedron to the surface area of the cube.
Transcribed Image Text:For every polyhedron there is a construction for a so called dual polyhedron by connecting together the centres of the faces. The diagram on the left below shows this construction for a cube that constructs an octahedron inside it. V₂. B A i 0 Choose an origin O to be the centre of the base of the cube and choose the i, j and k directions to be parallel to the faces of the cube. Let A be the centre of the face with positive i-coordinate and B be the centre of the face with positive j- coordinate, as shown in the right-hand diagram. Let the cube have a side length 2. (a) Write down OA and OB in terms of the unit vectors i, j and k. (b) Calculate OA OB and hence calculate the angle AOB. (c) Calculate OÀ X OB and hence calculate the ratio of the surface area of the octahedron to the surface area of the cube.
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