Question

4×5＋5×6＋6×7＋……＋35×36＋36×37

Answer 1

=(4^2+4)+(5^2+5)+...+(36^2+36)

=(1^2+2^2+...36^2)-(1+4+9)+(4+36)*(36-4+1)/2

=(2*36+1)(36+1)*36/6-14+660

=16852