# Math Help - Error on paper

1. ## Error on paper

A student of mine has handed me a test paper that was given to him at school. It seems to me there is a mistake on it, but I want to make absolutely sure. Here is the question:

Express $\frac{x^{2}-6x+1}{(x^2+1)(x^2-1)}$ in Partial Fractions

Hence show that $\frac{\mathrm{d} }{\mathrm{d} x}\left \{\frac{x^{2}-6x+1}{(x^2+1)(x^2-1)} \right \}$ when $x=2$ is $\frac{28}{45}$

I get $\frac{194}{225}$

3. ## Re: Error on paper

Hey grillage.

For this kind of thing I use a computer package to eliminate the human error aspect. Using Wolfram Alpha, we get:

d/dx((x^2 - 6x + 1)/((x^2+1)*(x^2-1))) - Wolfram|Alpha

Plugging in x = 2 gives us

dy/dx|x = 2 = 194/225 which is in agreement with your value.

4. ## Re: Error on paper

How does the partial fraction expansion help you to get the derivative?

- Hollywood