Question

Prove that for any natural value of n the value of the expression:

(5n+1)2–(2n–1)2 is divisible by 7

Answer 1

assume you mean
(5n+1)^2–(2n–1)^2
25 n^2 + 10 n + 1 - [ 4 n^2 -4 n + 1 ]
= 21 n^2 + 14 n + 0
= (1/7)(3 n^2 + 2 n)

Answer 2

3n^2+2n * 7
thats the answer