Question

If a - b = 5 and a² + b² = 31 then find the value of ab?

A. 4

B. 5

C. 2

D. 3

1. C
2. A
3. B
4. D

Answer 1

Correct Answer - Option 4 : D

Given:

a - b  = 5

a² + b² = 31

Formula used:

(a - b)² = a² + b² - 2ab

Calculation:

(a - b)2 = a2 + b2 - 2ab

⇒ 5² = 31 - 2ab

⇒ 25 = 31 - 2ab

⇒ 2ab = 31 - 25

⇒ 2ab = 6

⇒ ab = 3

∴ The value of ab is 3.