Question

a cube plus b cube
$\sin(?)$

Answer 1

Hello Debnath,
Here's your answer and derivation for that. Let me help you. My answer is ©.

(a  + b)³ = a³ + b³ + 3ab(a + b) = a³ + b³ + 3a²b + 3ab²
Therefore a³ + b³ = (a + b)³ - 3ab(a + b)

How ? :

(a + b)³ = (a + b)(a + b)² = (a + b)(a² + 2ab + b²) = a³ + b³ + 3ab(a + b).

Hope my answer helps you.