Question

1 2/1+3 6/1+5 1/12+7 1/20+9 1/30+11 1/42+13 1/56+15 1/72+17

Answer 1

题目打错了吧..应该是

1 1/2+3 1/6+5 1/12+7 1/20+9 1/30+11 1/42+13 1/56+15 1/72+17 1/90

=(1+2+...+17)+(1/(1*2)+1/(2*3)+1/(3*4)+.+1/(9*10)

=((1+17)*17/2)+((1/1-1/2)+(1/2-1/3)+.+(1/9-1/10))

=153+(9/10)

=153又9/10