“(1/4x1/6+1/6x1/8+1/8x1/10+1/10x1/12)x2的简便方法

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“(1/4x1/6+1/6x1/8+1/8x1/10+1/10x1/12)x2的简便方法
“(1/4x1/6+1/6x1/8+1/8x1/10+1/10x1/12)x2的简便方法

“(1/4x1/6+1/6x1/8+1/8x1/10+1/10x1/12)x2的简便方法
因为1/[n(n+2)]=1/2*[1/n-1/(n+2)]
所以1/4x1/6+1/6x1/8+1/8x1/10+1/10x1/12
=1/2*(1/4-1/6+1/6-1/8+1/8-1/10+1/10-1/12)
=1/2*(1/4-1/12)
=1/12
所以(1/4x1/6+1/6x1/8+1/8x1/10+1/10x1/12)x2=1/12*2=1/6

数学题1/4x1/5x1/6+1/5x1/6x1/7+1/6x1/7x1/8+.+1/98×1/99×1/100=? “(1/4x1/6+1/6x1/8+1/8x1/10+1/10x1/12)x2的简便方法 提问:1x1/2+1/2x1/3+1/3x1/4+1/4x1/5+1/5x1/6+1/6x1/7 用简便方法 简便计算题1x1/2+1/2x1/3+1/3x1/4+1/4x1/5+1/5x1/6+1/6x1/7 1/2X1/3+1/3X1/4+1/4X1/5+1/5X1/61/2X1/3+1/3X1/4+1/4X1/5+1/5X1/6简单的计算起来 数学题1/4x1/5x1/6+1/5x1/6x1/7+1/6x1/7x1/8+.+1/98×1/99×1/100=? 谢谢!要过程 1x1/2 +2x1/3 +3x1/4+ …… +8x1/9 +9x1/10简便方法计算 1/5X1/6+1/6X1/7+1/7X1/8+1/8X1/9+1/9X1/10简便方法如何解 1/5x1/6+1/6x1/7+1/7x1/8+1/8x1/9+1/9x1/10请问用简便方法如何解。 1/2X1/3+1/3X1/4+1/4X1/5+1/5X1/6+.+1/99X1/100=? 纺织机械 4x1 1511 single channel .56” 4x1 .1x1 这个4x1 1x1 奥数1/2x1/3x1/4+1/3x1/4x1/5+……+1/8x1/9x1/10 1/2x1/3+1/3x1/4+.1/8x1/9= 1/2X1/3+1/3X1/4+~+1/8x1/9=? 简便运算：1又6分之1X1又7分之1X1又8分之1X1又9分之1X1又10分之1 1又1/6x1又1/7x1又1/8x1又1/9x1又1/10= 不要直接给答案,要递等式 1x1/2+1/2x1/3+1/3x1/4+.+1/19x1/20=? (-1x1/2)+(-1/2x1/3)+(-1/3x1/4)+...+(-1/2004x1/2005)=?