Tuesday, March 30, 2010

`(3x^2 - 7x - 2)/(x^3 - x)` Write the partial fraction decomposition of the rational expression.

`(3x^2-7x-2)/(x^3-x)=(3x^2-7x-2)/[x(x+1)(x-1)]`


`(3x^2-7x-2)/(x^3-x)=A/x+B/(x+1)+C/(x-1)`



Multiply through by the LDC `x^3-x.`


`3x^2-7x-2=A(x^2-1)+Bx(x-1)+Cx(x+1)`


`3x^2-7x-2=Ax^2-A+Bx^2-Bx+Cx^2+Cx`


`3x^2-7x-2=(A+B+C)x^2+(-B+C)x-A`



Equate the coefficients of like terms. Then solve for A, B, and C.


`3=A+B+C`


`-7=-B+C`


`-2=-A`



`A=2`



`3=A+B+C`


`3=2+B+C`


`1=B+C`



Use the elimination method to solve for B and C.


`1=B+C`


`-7=-B+C`


_______________


`-6=2C`


`-3=C`



`1=B+C`


`1=B-3`


`4=B`



`A=2, B=4, C=-3`



`(3x^2-7x-2)/(x^3-x)=2/x+4/(x+1)-3/(x-1)`

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