7-3-41
X
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CC
On this problem, the first thing we have to do is factor the
denominator, which is the difference of cubes.
So we're going to get X -, 4 * X ^2 + 4 X plus 16.
Now we're going to rewrite those as our partial fractions.
So we're going to have a constant over the linear a / X
-, 4 + a linear over that non reducible quadratic.
So BX plus C over X ^2 + 4 X plus 16.
We're going to multiply everything through by the common
denominator.
So we're going to get -2 X squared plus eighteen X + 8
equaling a times the quantity X ^2 + 4 X plus 16 plus the
quantity BX plus C * X -, 4.
Then we're going to foil out and distribute on the right hand
side.
So we get AX squared plus 4AX plus 16A plus BX squared -4 BX
plus CX -4 C.
Now we need to group the coefficients of the squared
terms, the X ^2 terms on the left with the coefficients of
the X ^2 terms on the right.
So -2 equal A+B.
We need to group the X terms on the left with the X terms on the
right.
So 18 equal 4A minus four b + C and then we need to group the
terms with no X is on the left with the terms with no X is on
the right.
So 8 equaling sixteen a -, 4 C When I look at this, these new 3
equations, I want to figure out how to get rid of a variable.
We want to do either B or C because there's already B or C
missing in each in one of the three equations.
So if I get rid of the B, I'm going to take that top equation
and multiply it all the way through by 4 -8 equal 4A plus
4B.
When I add that with the second equation, we get 10 equaling 8A
plus C.
Now if we look at that third equation, it's all divisible by
4, so we get 2 equaling four a -, C If we add that directly
with that 10 equaling 8A plus C, we get 12 equal 12A or a is one.
Then I'm going to substitute the A equal 1 into one of the
equations.
I use the two equal four a -, C so 2 equal 4 * 1 -, C negative 2
equal negative C or C is 2.
And once I get my A and my C, I'm going to go back to the
original and find an equation with AB in it.
I used the top one -2 equal a + b or -2 equal 1 + b, so B is -3.
So our final answer is 1 / X -, 4 + -3 X plus 2 / X ^2 + 4 X
plus 16.