NCERT Solutions for Class 8 Maths Chapter 7 Cubes and Cube Roots Exercise 7.2

Ex.1  Find the value of 10³ - 9³ ?

Soln: 10³ - 9³

= 1+(3×10×9)=1+270=271

Therefore,

1000 -729 = 271.

Ex.2 Determine if 15625 is a perfect cube?

Soln: 

By prime factorisation,

15625 = 5 × 5 × 5 × 5 × 5 × 5 ………..combining the the factors in triplets

= 5³ × 5³ ………..by laws of exponents

= (5 × 5)³

= 25³ which is a perfect cube.

All the terms form triplets

Hence, 15625 is a perfect cube.