S.chand books class 8 maths solution chapter 21 Representing 3D shapes in 2D exercise 21

 EXERCISE 21

Question 1

The adjoining net is made up of two equilateral triangles and three rectangles
(i) Name the solid it represents
(ii) How many faces,edges and vertices does this solid have ?

Sol :

Question 2

For each solid, count the number of faces , vertices and edges. Check if the Euler's rule is true for each one.
(i)
(ii)
(iii)
(iv)

Sol :

Question 3

Name the solids that have
(i) 4 faces
(ii) 1 curved surface
(iii) 6 faces
(iv) 5 faces and 5 vertices
(v) 8 triangular faces
(vi) 6 rectangular faces and 2 hexagonal faces.

Sol :

Question 4

Name the different plane shapes needed to draw the net of a
(i) cube
(ii) triangular prism
(iii) triangular pyramids

Sol :

(i) Square

(ii) Rectangle , Triangle

(iii) Triangle

(iv) Circle, Rectangle

Question 5

Given here is the net of an octahedron with numbers 0 and 7 on the faces. Enlarge these on a cardboard to make a model.
(i) How many faces,edges and vertices does this solid have ?
(ii) Check whether Euler's rule is true for the octahedron or not .

Sol :

Question 6

Draw the 2D representation of a
(i) cube 


(ii) triangular prism

Sol :

Question 7

On an isometric dotted paper draw the following shapes.
(i) cube (ii) cuboid (iii) hexagonal prism (iv) pentagonal prism

Sol :

Question 8

Name the solid that would be formed by each net:

(i) fig
(ii) fig
(iii) fig

Sol :

(i) Triangular Prism
(ii) Square Pyramid 
(iii) Hexagonal Pyramid