Question

ab = 36, a − b = 9 ∴ a³ − b³ = ______.

विकल्प

• 243

• 1701

• 729

• 765

Answer 1

ab = 36, a − b = 9 ∴ a³ − b³ = 1701.

Explanation:

a³ − b³ = (a − b) (c)

Let’s find a² + b²:

a² + b² = (a − b)² + 2ab

a² + b² = (9)² + 2(36)

a² + b² = 81 + 72

a² + b² = 153

Then,

a² + ab + b² = a² + b² + ab

= 153 + 36

= 189

Hence, 

a³ − b³ = 9 × 189

a³ − b³ = 1701