# RS Aggarwal Class 8 Math Nineteenth Chapter Three-Dimensional Figures Exercise 19B Solution

## EXERCISE 19B

**(1) Define Euler’s relation between the number of faces, number of edges and number of vertices for various 3-dimensional figures.**

Ans: In a 3-dimensional figure, let the number of faces be F; the number of edges be E and the number of vertices be V.

Then, the Euler’s relation is given by

# F – E + V = 2

**(2) How many edges are there in a **

(i) Cuboid = 12 edges

(ii) Tetrahedron = 6 edges

(iii) Triangular prism = 9 edges

(iv) Square pyramid = 8 edges

**(3) How many faces are there in a**

(i) Cube = 6 faces

(ii) Pentagonal prism = 7 faces

(iii) Tetrahedron = 4 faces

(iv) Pentagonal pyramid = 6 faces

**(4) How many vertices are there in a **

(i) Cuboid = 8 vertices

(ii) Tetrahedron = 4 vertices

(iii) A triangular prism = 10 vertices

(iv) A square pyramid = 5 vertices