gunakan prinsip induksi matematika untuk membuktikan kebenaran formula yang diberikan (n bilangan asli) 1.2+2.3+3.4+...+n.(n+1)=n(n+1)(n+2)/3

1.2+2.3+3.4+...+n(n+1) = n(n+1)(n+2)/3
n = k
1.2+2.3+3.4+...+k(k+1) = k(k+1)(k+2)/3
n = k + 1
1.2+2.3+3.4+...+k(k+1) +(k+1)(k+2)= (k+1)(k+2)(k+3)/3
k(k+1)(k+2)/3 + (k+1)(k+2) = (k+1)(k+2)(k+3)/3
{k(k+1)(k+2) + 3(k+1)(k+2)} /3 = (k+1)(k+2)(k+3) / 3
{(k+1)(k+2) (k +3)}/3 = (k+1)(k+2)(k+3) /3