Question

1*2/1+2*3/1+3*4/1+...+8*9/1+9*10/1简算

Answer 1

二分之一写作1/2

1/1x2+1/2x3+1/3x4+...+1/9x10

=(1-1/2)+(1/2-1/3)+(1/3-1/4)+...+(1/9-1/10)

=1-1/10

=9/10