Question

2*2+4*4+6*6+8*8+...+30*30=?

Answer 1

2*2+4*4+6*6+8*8+...+30*30

=2^2*(1^2+2^2+3^2+...+15^2)

=4*15*(15+1)*(2*15+1)/6

=4960

1^2+2^2+3^2+.+n^2=n(n+1)(2n+1)/6