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# Partial fractions c3 help..EASY!! watch

1. how do i solve this:

I know to get B we let x=1 and solve to get B=1/3

But to get A and C do we have to equate coefficients?

Would equating x terms give: -A + B - 2C = 0 ?
and then equating constant terms: A + 2B + C = 1

then we add the two to remove the x term then sub 1/3 in for B to allow us to get C.

But I get that C=0?

How can this be? What have i done wrong?

2. Let

Comparing coefficients of

Let

This is a slightly different method, but it gives again.

What was the original fraction?
3. (Original post by GingerCodeMan)

Let

Comparing coefficients of

Let

This is a slightly different method, but it gives again.

What was the original fraction?
many thanks
4. You should have written

.

Tut-tut. Now C wont be zero.
5. Understand?

....But you wrote down instead. That's where the mistake started.
6. Starting fom the beginning

Multiplying both sides by gives

.

Setting gives . Setting gives . Lastly, equating terms gives .

So , and .
7. (Original post by Mr Tall)
how do i solve this:

(Original post by GingerCodeMan)

(Original post by steve44)

.

is how you get the identity sign

"What was the original fraction?"

Mr Tall said:

""

This fraction leads to the equation

instead (look at the first term on the LHS of these two equations). Mr Tall made a typo here, this is the mistake!!!

You cant possibly end up with ( corresponding to the term in the partial fraction expansion) because otherwise you would have is divergent for while wouldn't be!!

This is all about a typo - that's all I'm saying. Correct this typo and then you dont get C=0.

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Updated: January 20, 2014
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