Question 26 1 1 of the third edition of seventh grade mathematics weekly.
1*2+2*3+3*4+……+n(n+ 1)=( 1^2+ 1)+(2^2+2)+(3^2+3)+……+(n^2+n)=( 1^2+2^2+3^2+……+n^2)+( 1+2+3+……+n)=[n(n+ / kloc-0/)(2n+ 1)]/6+[n(n+ 1)]/2 =[n(n+ 1)(5n+2)]/6 1 * 2+2 * 3+3 * 4+ 100 * 10 1 = 1 2+ / Kloc-0/+2+2+3 2+100+N2 = n (n+1) (2n+1)/61+2+3+n = n (n+/kloc 1*2+2*3+3*4+ 100* 10 1= 100* 10 1*20 1/6+ 100* 10 1/2=343400