Question

简便计算，急啊 ①1×2+2×3+3×4+……+59×60 ②1×2+2×3+3×4+……+199

Answer 1

①

1×2+2×3+……+59×60

=((1×2×3-0×1×2)+(2×3×4-1×2×3)+……+(59×60×61-58×59×60))÷3

=59×60×61÷3

=71980