NCERT Solutions for Class 8 Maths Chapter 9 Algebraic Expressions and Identities Exercise 9.2

Ex.1  Find the product using a suitable identity : (3xy – 5)²

Soln: From the identities we know, 

(a – b)² = a² – 2ab + b²

Applying in the given equation we get, 

(3xy – 5)² = (3xy)² – 2 × 3xy × 5 + (5)²

= 9x²y² – 30xy + 25

Ex.2 Find the areas of a rectangle with the following monomials as their lengths and breadths respectively :(3mn, 4np)

Soln: Area of the rectangle = Length × Breadth

Therefore, in this case,

Length, L=3mn

Breadth, B=4np

Area=L * B

= (3mn) × (4np)

= (3 × 4) × (mn) × (np)

= 12 × m × (n × n) × p

= 12mn²p