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C4 - Help needed: Binomial Expansion/Partial Fractions

Hi, I'm on Edexcel (C4)trying to learn the binomial expansion, but I'm stuck on a seemingly straight forward questions :s-smilie:

Express -2x/(2+x)^2 as a partial fraction

So far, I've done:

-2x/(2+x)^2 = A/(2+x) + B/(2+x)^2

= A(2+x)/(2+x)^2 + B/(2+x)^2

This is where it seems to go wrongs.

Help please!
Thanks

Reply 1

vc94

Equating numerators:
-2x = A(2+x) + B

You know the rest of the method?

Reply 2

AFCAARLP

You do what vc94 said and then equating coefficients you get Ax = -2x, so A=-2, and then subbing that into the equation gives you -2x = -4 - 2x + B, so B = 4

Simples :smile:

Reply 3

Shenron

Original post by vc94

Equating numerators:
-2x = A(2+x) + B

You know the rest of the method?

Original post by AFCAARLP

You do what vc94 said and then equating coefficients you get Ax = -2x, so A=-2, and then subbing that into the equation gives you -2x = -4 - 2x + B, so B = 4

Simples :smile:

Thanks, I understand now!

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C4 - Help needed: Binomial Expansion/Partial Fractions

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