Here is the original problem: $\int \frac{3x^2-2}{x^2-4x-12}\ \mathrm dx$

After doing polynomial division and factoring the denominator I got this:

$$\int 3 + \frac{12x+36}{(x-6)(x+2)}\ \mathrm dx$$

Then using partial fraction decomposition I got the following:

$$\int 3\ \mathrm dx+ \frac{27}{2}\int \frac{\ \mathrm dx}{x-6} -\frac{3}{2}\int \frac{\ \mathrm dx}{x+2}$$

For the final answer I got this:


But it says my answer is incorrect. Can you all spot my error or should I provide more details?

  • 3
    $\begingroup$ You factored wrong : It should be $$3 + \frac{12x + 34}{(x-6)(x+2)}$$ $\endgroup$ – Prahlad Vaidyanathan Oct 19 '13 at 3:11
  • $\begingroup$ @PrahladVaidyanathan wow... thank you :( $\endgroup$ – hax0r_n_code Oct 19 '13 at 3:13

You did the calculation wrong. $$\frac{3x^2-2}{x^2-4x-12} = \frac{3(x^2-4x-12)-2+12x+36}{x^2-4x-12} = 3+\frac{12x+34}{x^2-4x-12}$$

Now, try to evaluate your integral


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