Respuesta :

you can prove it by using synthetic division and divide x^n - a^n by x-a

First step
x^n - a^n  - x^n-1 (x-a) = x^n-1 a - a^n

Second step
x^n-1 a - a^n  - x^n-2 a (x-a ) = x^n-2 a^2 - a^n
 . . .until the exponent of x become 0

Hope this helps