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# C4 partial fractions help. watch

1. f(x) = x2+1
....(1+x)(3-x)

= A + B/(1-x) + C/(3-x)

I can get B and C but why does A=-1?

Thanks
2. (Original post by sb1986)
f(x) = x2+1
....(1+x)(3-x)

= A + B/(1-x) + C/(3-x)

I can get B and C but why does A=-1?

Thanks

The constant 'A' is there because the degree of the numerator is greater than or equal to the degree of the denominator. You can find A by setting or expanding the denominator and using algebraic long division.
You've typed either one of the terms in the denominator of f(x) incorrectly or the second term of the partial fractions incorrectly.

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