Question

急救 一个小学数学题 在线等1/1*2+1/2*3=4/61/1*2+1/2*3+1/3*4=9/121/1*2+1/2

Answer 1

1/1*2+1/2*3=2^2/2*3=4/6

1/1*2+1/2*3+1/3*4=3^2/3*4=9/12

1/1*2+1/2*3+1/3*4+...1/1997*1998=1997^2/1997*1998=3988009/3990006