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C3 Rational Expression question

jessyjellytot14

Hi can someone explain how to do this please?

ImageUploadedByStudent Room1473517657.868449.jpg

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Reply 1

zetamcfc

\frac{2x +5}{x+3} = \frac{A(x+3)}{x+3} + \frac{B}{x+3}

Hope that helps, @jessyjellytot14

Reply 2

RDKGames

Study Forum Helper

Original post by jessyjellytot14

Hi can someone explain how to do this please?

ImageUploadedByStudent Room1473517657.868449.jpg

Posted from TSR Mobile

You can multiply both sides of the identity by (x+3) then proceed to expand and compare coefficients in terms of A and B because they must be the same on both sides of the identity.

(edited 7 years ago)

Reply 3

jessyjellytot14

Original post by RDKGames

You can multiply both sides of the identity by (x+3) then proceed to expand and compare coefficients in terms of A and B because they must be the same on both sides of the identity.

Okay I tried multiplying each side by (x+3) but i'm not sure if you meant like this...
ImageUploadedByStudent Room1473519891.374618.jpg

When I compare the coefficients I just end up with 2x+5/x+3 again or something that is not on the mark scheme

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Reply 4

RDKGames

Study Forum Helper

Original post by jessyjellytot14

Okay I tried multiplying each side by (x+3) but i'm not sure if you meant like this...
ImageUploadedByStudent Room1473519891.374618.jpg

When I compare the coefficients I just end up with 2x+5/x+3 again or something that is not on the mark scheme

Posted from TSR Mobile

You multiplied the denominator by (x+3), no need to do that. Just multiply both sides of the identity by the denominator of the LHS so you can lose it.

Reply 5

jessyjellytot14

Original post by RDKGames

You multiplied the denominator by (x+3), no need to do that. Just multiply both sides of the identity by the denominator of the LHS so you can lose it.