1/35+1/63+1/99+1/143=1/(5×7)+1/(7×9)+1/(9×11)+1/(11×13)=1/2×(1/5-1/7)+1/2×(1/7-1/9)+1/2×(1/9-1/11)+1/2×(1/11-1/13)=1/2×(1/5-1/7+1/7-1/9+1/9-1/11+1/11-1/13)=1/2×(1/5-1/13)=1/2×(13/65-5/65)=1...为啥会有1/21/n-1/(n+2)
=(n+2)/[n(n+2)]-n/[n(n+2)]
=2/[n(n+2)]
∴1/[n(n+2)]=1/2×[1/n-1/(n+2)]
猜你喜欢
- 10度的水和0度的冰放在0度的房间里
- 2let me have your cell 是什么意思.有个老外在邮件里这么说.是cell phone 简写了么?
- 3一个质数加上6,减去6还是质数.已知这个质数在20以内,你知道这个质数可能是多少吗?
- 4有一堆煤.第一天运了五分之二,再运50吨就比这吨煤的一半多30吨,求这吨煤?
- 5Every morning in the school,when we see that he is so tired after a night’s “busy working”,we really feel sad.的翻译
- 6概率题:设A.B是两个任意事件,且P(A)=0.5,P(B)=0.6,P(B/A)=0.8,则P(A∪B)=求详细指教?
- 7如果代数式2a²﹢3a﹢1的值是6,则代数式6a²﹢9a﹢5的值是().
- 8在1.0L溶液为1.6molNa2CO3溶液中,能否使0.10mol/L的BaSO4溶液完全转化为BaCO3 Ksp(BaSO4)=1.08×10-10
- 9将电阻R1、R2串联在电压为4.5V的电源上,已知R1的电阻为5Ω,R2两端的电压为3V,求电路中的总电阻和通过R2
- 10当a小于-2分之1时,根号下(2a+1)的平方=