一数学题1111
来源:百度知道 编辑:UC知道 时间:2024/06/15 14:30:02
(1)知1*2 /1=1-2/1 2*3 /1=2/1-3/1 3*4 /1=3/1-4/1 求2/1+6/1+12/1+20/1+…+90/1
(2)知2/1=1-2/1 6/1=2/1-3/1 12/1=3/1-4/1 求 2/1-6/1-12/1-20/1-30/1-42/1-…-132/1
(2)知2/1=1-2/1 6/1=2/1-3/1 12/1=3/1-4/1 求 2/1-6/1-12/1-20/1-30/1-42/1-…-132/1
老师上课 没认真听 ~~ 1
1. 1/2+1/6+1/12+1/20+...+1/90
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+...+1/9-/10
=1-1/10=9/10
2. 1/2-1/6-1/12-1/20-1/30-1/42-...-1/132
=1-1/2-1/6-1/12-1/20-1/30-1/42-...-1/132
=1-(1/2+1/6+1/12+1/20+...+1/132)
=1-(1-1/2+1/2-1/3+1/3-1/4+1/5-1/6=...+1/11-1/12)
=1-(1-1/12)=1/12
2
错位相减
1.……=1-1/10=1/10
2.……=1-1/12=11/12
怎么样 我牛吧?????????
错位相减
1.……=1-1/10=1/10
2.……=1-1/12=11/12
1. 1/2+1/6+1/12+1/20+...+1/90
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+...+1/9-/10
=1-1/10=9/10
2. 1/2-1/6-1/12-1/20-1/30-1/42-...-1/132
=1-1/2-1/6-1/12-1/20-1/30-1/42-...-1/132
=1-(1/2+1/6+1/12+1/20+...+1/132)
=1-(1-1/2+1/2-1/3+1/3-1/4+1/5-1/6=...+1/11-1/12)
=1-(1-1/12)=1/12