n=1, left =1*2=2, right =1*2*3/3 =2,
assume n = k , we have sum of i(i+1) from 1 to k = k(k+1)(k+2)/3k+2)/3
n=k+1 sum of i(i+1) from 1 to k+1 = k(k+1)(k+2)/3 + (k+1)(k+2) = (k+1)（k+2)[k/3+1)
thus the identify holds for n = k+1,
from principle of mathematical induction, the identity holds for every n>0
Content will be erased after question is completed.
Enter the email address associated with your account, and we will email you a link to reset your password.
Forgot your password?