Answer:
2+4+6+...+2k+2(k+1) = k(k+1) + (k+1)(k+1)
Explanation:
Proved case for n
2+4+6+...+2n = n(n+1) ................(1)
for n = k + 1, we replace n by k and add n = k+1 on both sides (
2+4+6+...+2k+2(k+1) = k(k+1) + 2(k+1))
rearrange by factoring the right-hand-side
2+4+6+...+2k+2(k+1) = (k+1)(k+2)
which if we substitute n=k+1, we get back
2+4+6+...+2(n-1) + 2(n) = n(n+1) ...............(2)
This means that equation (1) is applicable to case n+1, and the proof by induction is completed.