带数求值！^-^
还有一选择题O(∩_∩)O
下列运算正确的是 （ ）
A.a/a-b-b/b-a=1 B.m/a-n/b=m-n/a-b
C.b/a-b+1/a=1/a D.2/a-b-a+b/a^2-b^2=1/a-b
x^2-y^2/x^2+2xy+y^2-x+y/x-y,其中x=1,y=-3
答案:2 悬赏:60 手机版
解决时间 2021-04-08 10:48
- 提问者网友：轻浮
- 2021-04-08 07:08
最佳答案
- 五星知识达人网友：刀戟声无边
- 2021-04-08 07:17
x^2-y^2/x^2+2xy+y^2-x+y/x-y
=(x+y)(x-y)/(x+y)²-(x+y)/(x-y)
=(x-y)/(x+y)-(x+y)/(x-y)
=-4xy/(x²-y²)
当x=1，y=-3时
原式=12/(1-9)=-3/2
D.2/a-b-a+b/a^2-b^2=1/a-b
=(x+y)(x-y)/(x+y)²-(x+y)/(x-y)
=(x-y)/(x+y)-(x+y)/(x-y)
=-4xy/(x²-y²)
当x=1，y=-3时
原式=12/(1-9)=-3/2
D.2/a-b-a+b/a^2-b^2=1/a-b
全部回答
- 1楼网友：神鬼未生
- 2021-04-08 08:26
(x^2+2xy+y^2/x^2-xy)/{[-y(x+y)/(x-y)^2]/(1/x+y)}
=[（x+y）^2/x(x-y)]/{[-y(x+y)/(x-y)^2]*(x+y)}
=[(x+y)^2/x(x-y)]/[-y(x+y)^2/(x-y)^2]
=[(x+y)^2*(x-y)^2]/[x(x-y)*(-y)(x+y)^2]
=-(x-y)/xy
=(y-x)/xy
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