6/1*2+6/2*3+6/3*4+~6/66*67

问题描述:

6/1*2+6/2*3+6/3*4+~6/66*67

6/1*2+6/2*3+6/3*4+……+6/66*67
=6*(1-1/2+1/2-1/3+1/3-1/4+……+1/66-1/67)
=6*(1-1/67)
=6-6/67
=5又61/67