Question

2分之一加6分之一加12分之一加20分之一加30分之一等于多少?急用!在线等答案!好答案追加分!

Answer 1

您好!

公式：1/[n*(n+1)]=1/n-1/(n+1)

原式=1/2+1/6+1/12+1/20+1/30

=1/(1*2)+1/(2*3)+1/(3*4)+1/(4*5)+1/(5*6)

=(1-1/2)+(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)

=1-1/6

=5/6