Question

Use a suitable identity to get each of the following products

a) (7a - 9b)2​

Answer 1

Given:

The expression -

• (7a - 9b)²

What To Find:

We have to find

• Product using a suitable identity.

Solution:

The expression,

⇒ (7a - 9b)²

It is in the form of (a - b)² = a² + b² - 2ab,

⇒ Where,

• a = 7a
• b = 9b

So it will be,

⇒ (7a)² + (9b)² - 2(7a × 9b)

Find the square of (7a)²,

⇒ 49a² + (9b)² - 2(7a × 9b)

Find the square of (9b)²,

⇒ 49a² + 81b² - 2(7a × 9b)

Find (7a × 9b),

⇒ 49a² + 81b² - 2(63ab)

Find 2(63ab),

⇒ 49a² + 81b² - 126ab

Identity Used:

• (a - b)² = a² + b² - 2ab

Final Answer:

∴ Hence, the answer is 49a² + 81b² - 126ab.