Question

1/1x2+1/2x3+13*4+1/4x5=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5=1-1/5=4/5用上方法求1/2-1/6-1/12-1/20-1/30-1/42

Answer 1

1/2-1/6-1/12-1/20-1/30-1/42

=1/2-1/6-1/12-1/20-1/30-1/42
=1-1/2-1/6-1/12-1/20-1/30-1/42
=1-（1/2+1/6+1/12+1/20+1/30+1/42）
=1-(1/1x2 + 1/2x3+...+1/6x7)
=1-(1- 1/7)
=1/7

Answer 2

原式=1/2-(1/6+1/12+1/20+1/30+1/42)

=1/2-(1/2x3+13*4+1/4x5+1/5x6+1/6x7)
=1/2-(1/2-1/3+1/3-1/4+……+1/6-1/7)
=1/2-(1/2-1/7)
=1/7

追问

好像你没有按以上顺序吧...

追答

没错