微云显示下载外链次数:多道数学题目7点就关闭问题了

1.
(x-1/x)/(x+1/x-2)
=(x^2-1)/(x^2+1-2x)
=(x+1)(x-1)/(x-1)^2
=(x+1)/(x-1)

2.
x+1=(a+1+a-1)/(a-1)=2a/(a-1)
(x+1)/x=2a/(a+1)

3.
(3a-6b)/(a+b)-(5a-6b)/(a-b)-(4a-5b)/(a+b)-(7a-8b)/(b-a)
=(3a-6b)/(a+b)-(4a-5b)/(a+b)-(5a-6b)/(a-b)+(7a-8b)/(a-b)
=(3a-6b-4a+5b)/(a+b)+(7a-8b-5a+6b)/(a-b)
=(-a-b)/(a+b)+(2a-2b)/(a-b)
=-1+2
=1

4.
{(a+b)/(a-b)+b/(b-a)}÷1/(a+b)
=(a+b-b)/(a-b)÷1/(a+b)
=a*(a+b)/(a-b)
=(1/2)*(1/2+1/3)/(1/2-1/3)
=5/2

5.
A/x+B/(x-1)+C/(x+2)
=A(x-1)(x+2)/x(x-1)(x+2)+Bx(x+2)/x(x-1)(x+2)+Cx(x-1)/x(x-1)(x+2)
=[A(x^2+x-2)+(Bx^2+2Bx)+(Cx^2-Cx)]/x(x-1)(x+2)
=[(A+B+C)x^2+(A+2B-C)x-2A]/x(x-1)(x+2)
A+B+C=0
A+2B-C=2
-2A=3
A=-3/2
B=5/3
C=-1/6

6.
7/2x^2+6x-11-2x^2/9-x^2+2
看不懂，应该有括号吧？

7.
x^2-3x+1=0
x-3+1/x=0
x+1/x=3
(x+1/x)^2=9
x^2+2+1/x^2=9
x^2+1/x^2=7

8.
2xy/(x^2-y^2)-x/(x+y)+y/(y-x)
=2*3*2/(9-4)-3/(2+3)+2/(2-3)
=12/5-3/5-2
=-1/5

好麻烦啊，只能慢慢做了！！
1、x-2/x
2、2a^2+2/(a+1)(a-1）
3 1
4 原始的式子得a/(a-b)*a/(ab+1） 得到了-3/11
5、不算太会，只能告诉你的结果了5x+5-6/x
剩下我没时间了，我只能做到这了阿

1.
(x-1/x)/(x+1/x-2)
=(x^2-1)/(x^2+1-2x)
=(x+1)(x-1)/(x-1)^2
=(x+1)/(x-1)

2.
x+1=(a+1+a-1)/(a-1)=2a/(a-1)
(x+1)/x=2a/(a+1)

3.
(3a-6b)/(a+b)-(5a-6b)/(a-b)-(4a-5b)/(a+b)-(7a-8b)/(b-a)
=(3a-6b)/(a+b)-(4a-5b)/(a+b)-(5a-6b)/(a-b)+(7a-8b)/(a-b)
=(3a-6b-4a+5b)/(a+b)+(7a-8b-5a+6b)/(a-b)
=(-a-b)/(a+b)+(2a-2b)/(a-b)
=-1+2
=1

4.
{(a+b)/(a-b)+b/(b-a)}÷1/(a+b)
=(a+b-b)/(a-b)÷1/(a+b)
=a*(a+b)/(a-b)
=(1/2)*(1/2+1/3)/(1/2-1/3)
=5/2

5.
A/x+B/(x-1)+C/(x+2)
=A(x-1)(x+2)/x(x-1)(x+2)+Bx(x+2)/x(x-1)(x+2)+Cx(x-1)/x(x-1)(x+2)
=[A(x^2+x-2)+(Bx^2+2Bx)+(Cx^2-Cx)]/x(x-1)(x+2)
=[(A+B+C)x^2+(A+2B-C)x-2A]/x(x-1)(x+2)
A+B+C=0
A+2B-C=2
-2A=3
A=-3/2
B=5/3
C=-1/6
7/2x^2+6x-11-2x^2/9-x^2+2
8.
2xy/(x^2-y^2)-x/(x+y)+y/(y-x)
=2*3*2/(9-4)-3/(2+3)+2/(2-3)
=12/5-3/5-2
=-1/5

好费脑壳哟,各人想法哈,帮不了你