# Partial FractionsWatch

#1
Hi, 1st question of A2 Maths.

Split the following into partial fractions:

25/(x^3 -3x - 4)

Working:

5/(x-4) +/- 5/(x+1)

How do I know weather the symbol in between is a plus or a minus the correct symbol is a minus
0
10 years ago
#2
I assume that's supposed to be an x^2 instead of an x^3...

Well basically you say that

Then you get a common denominator on the right hand side (which of course will be the same as the denominator on your left).

So 25 = A(x + 1) + B(x - 4)

25 + 0x = Ax + Bx + A - 4B

Ax + Bx = 0x

25 = A - 4B

Can you figure it out from here?
0
#3
Yes I understand all that so basically if A is a -ve value the sign in between is -ve but we write A as being positive
0
10 years ago
#4
Well, how have you got to ? (I assume you mean x^2 in the denominator rather than x^3).

You've presumably got to - how do you find A and B from here?

EDIT: Okay, so I was a tad slow...

Yes I understand all that so basically if A is a -ve value the sign in between is -ve but we write A as being positive
If you find a partial fraction's numerator to be negative, say, -2, then you will have something like - which equals . I think you've got the right idea.
0
10 years ago
#5
Yes I understand all that so basically if A is a -ve value the sign in between is -ve but we write A as being positive
I don't get what you mean.

You've said that and you know how to find values for A and B... so just sub them back into .
0
#6
Adje if thats the right way it makes sense just how I imagined it to be
0
10 years ago
#7
If B for instance is negative then you would put the partial fraction on the left (minus) the partial fraction for the constant B. I can't explain it properly m sorry"
0
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