5/2x3-7/3x4+9/4x5-11/5x6+13/6x7-15/7x8
=1/2+1/3-1/3-1/4+1/4+1/5-1/5-1/6+1/6+1/7-1/7-1/8
=1/2-1/8
=3/8
=1/2+1/3-1/3-1/4+1/4+1/5-1/5-1/6+1/6+1/7-1/7-1/8
=1/2-1/8
=3/8
...3x4分之7 4x5分之9-5x6分之11 6x7分之13-7x8分之15怎简便运
裂项法：5\/2x3-7\/3x4+9\/4x5-11\/5x6+13\/6x7-15\/7x8 =1\/2+1\/3-1\/3-1\/4+1\/4+1\/5-1\/5-1\/6+1\/6+1\/7-1\/7-1\/8 =1\/2-1\/8 =3\/8
5\/2x3-7\/3x4+9\/4x5-11\/5x6+13\/6x7-15\/7x8
裂项法：5\/2x3-7\/3x4+9\/4x5-11\/5x6+13\/6x7-15\/7x8 =1\/2+1\/3-1\/3-1\/4+1\/4+1\/5-1\/5-1\/6+1\/6+1\/7-1\/7-1\/8 =1\/2-1\/8 =3\/8
1×2×3分之1+2×3×4分之1+3×4×5分之1+...+13×14×15分之1 简便计...
解：（4）原式=1\/3（1-1\/4）+1\/3（1\/4-1\/7）+1\/3（1\/7-1\/10）+1\/3（1\/10-1\/13）+1\/3（1\/13-1\/16）=1\/3（1-1\/4+1\/4-1\/7+1\/7-1\/10+1\/10-1\/13+1\/13-1\/16）=1\/3（1-1\/16）=1\/3*15\/16 =5\/16 ...
数学题目:1\/2X3\/4X5\/6X7\/8X9\/10……99\/100算此题目,有没有什么规律...
A=1\/2X3\/4X5\/6X7\/8...X99\/100 假设一个数B B=2\/3X4\/5X6\/7X8\/9...X98\/99 则AXB=1\/100 而1\/100=1\/10X1\/10 因为B＞A,所以B＞1\/10 则A＜1\/10 这个只能做个简单的判断，很难计算出准确数据的
怎样用简便方法计算下列各题?
①1\/2X1\/15+1\/3X1\/2 =1\/2×1\/3×(1\/5+1) =1\/6×6\/5 =1 ②5\/6X5\/9+5\/9X1\/6 =1\/6×5\/9×(5+1) =5\/9 ③3\/9X7\/16X2\/9 =1\/3×7\/8×1\/9 =7\/216 ④2\/5X4X3\/4 =2\/5×3 =6\/5 =1又1\/5 ⑤4\/5X7\/9X8\/5 =224\/225 ⑥5\/7X16...
1x2\/3-3x4\/5+5x6\/7-7x8\/9+9x10\/11=??
1x2\/3－3x4\/5+5x6\/7-7x8\/9+9x10\/11 =2\/3 -12\/5 +30\/7 -56\/9 +90\/11 =(2\/3 -56\/9)-(12\/5 -30\/7)+90\/11 =-50\/9 -(84-150)\/35 +90\/11 = -50\/9 +66\/35+90\/11 =(-50x35+66x9)\/315 +90\/11 =-1156\/315 +90\/11 =(-1156x11+90x315)\/3465 =15634\/3465...
数学题目:1\/2X3\/4X5\/6X7\/8X9\/10……99\/100算此题目,有没有什么规律...
A=1\/2X3\/4X5\/6X7\/8...X99\/100 假设一个数B B=2\/3X4\/5X6\/7X8\/9...X98\/99 则AXB=1\/100 而1\/100=1\/10X1\/10 因为B＞A,所以B＞1\/10 则A＜1\/10 这个只能做个简单的判断，很难计算出准确数据的
5555十552x33x44x55x66x77x8
3\/10 [1\/3(1-1\/4+1\/4-1\/7+1\/7-1\/10)]=1\/3*9\/10(题目错了吧~）4\/9 [1\/2(1-1\/3+1\/3-1\/5+1\/5-1\/7+1\/7-1\/9)]=1\/2*8\/9 1\/10 1\/5-1\/6+1\/6-1\/7+……+1\/9-1\/10=1\/5-1\/10 （题目有错了吧,每个乘号应该隔着一个加号~~）
数学题 用简便方法计算 急急急!!!
1又2分之1乘1又3分之1乘1又四分之1乘1又5分之1乘1又6分之1乘1又7分之1乘1又8分之1乘1又9分之1乘1又10分之1 =2分之3×3分之4×4分之5×。。。×9分之10×10分之11 =2分之11
2x3分之一+3x4分之一+4x5分之一+5x6分之一+...+20x21分之一=几分之几...
42分之19 分析：2x3分之一可变为1\/2-1\/3,3x4分之一可变为1\/3-1\/4...20x21分之一可变为1\/20-1\/21,相加即为1\/2-1\/3+1\/3-1\/4+1\/4-1\/5+...+1\/20-1\/21=1\/2-1\/21=19\/42 同理5x7分之一可变为1\/2x(1\/5-1\/7),7x9分之一可变为1\/2x(1\/7-1\/9),35x37分之一可...
