Partial Fractions

Can anyone tell me why doing two different methods yields two different answers? Thanks

Because your partial fractions break down is incomplete, and should be:

$\displaystyle\frac{x^2-4x}{(x-2)(x+1)^2}\equiv\frac{A}{x-2}+\frac{B}{(x+1)^2}+\frac{C}{x+1}$

Cheers but why was my method wrong? It seems right :/

If you plug in only two values, you'll get a solution as there are only two unknowns, when you use just A and B. It's when you try a third value, that the problem shows up.

If you plug in only two values, you'll get a solution as there are only two unknowns, when you use just A and B. It's when you try a third value, that the problem shows up.

When I plug in x=4, it gives me 3x10^-5 but how can this be, as plugging it into the original formula clearly gives you zero. All other numbers work though...

I know, but why is that?


Posted from TSR Mobile

How on earth do you get 3x1o^-5?

I get 0.

For the partial fractions one I get that. Every other number works fine.


Posted from TSR Mobile

Post your working then.

This is for x=4.

Should have guessed it was a calculator.

3e-15.

Well it's a problem with the accuracy of the calculator. It's stored the numbers as decimals, and all it can do is approximate the last digit.
If you can get it to work in fractions, it should come out correctly.

Should have guessed it was a calculator.

3e-15.

Well it's a problem with the accuracy of the calculator. It's stored the numbers as decimals, and all it can do is approximate the last digit.
If you can get it to work in fractions, it should come out correctly.

...

Very Strange.

Well the problem is the calculator, or how you're using it, and not having one of that model myself, I can't help.

But the maths, by hand, is correct, 0.