1/(x+2)=1/(x-2)-(6-x)/(3x-12)

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1/(x+2)=1/(x-2)-(6-x)/(3x-12)
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1/(x+2)=1/(x-2)-(6-x)/(3x-12)
1/(x+2)=1/(x-2)-(6-x)/(3x-12)

1/(x+2)=1/(x-2)-(6-x)/(3x-12)
1.(1/2-x)-1=(1/x-2)-(6-x/3x^2-12)
-3x+2-(3x^2-12)= 3(x+2)-(6-x)
解得,x1=-3,x2=2/3
2.(1/1-x)-1=(3x-x^2/1-x^2)
x+1-(x+1)(x-1)=x(3-x)
2x^2-2x=0
2x(x-1)=0
∴2x=0或(x-1)=0
∴x1=0,x2=1
①把x1=0代入(x+1)(x-1)得
(x+1)(x-1)=-1
②把x2=1代入(x+1)(x-1)得
(x+1)(x-1)=0
∴x=1为增根,舍.
∴x=0
3.x^4-2x^2-15=0
(x^2+3)(x^2-5)=0
∴x^2=-3或x^2=5
∵x^2≥0
∴x^2=3,无解
∴x^2=5
∴x1,2=±√5
4.√(2x^2+7x)-2=x
2x^2+7x=x^2+4x+4
x^2+3x-4=0
解得,x1=-4,x2=1