# Thread: I can't remember how to solve from first principles...

1. ## I can't remember how to solve from first principles...

Thank you!

2. Try factoring the denominator. Or did you mean the delta-epsilon method?

3. oooh.. thank you.
1/14

4. Correct.

5. For the future use of metaname90 (and anyone else): the only reason you cannot just put x= 4 into $\frac{x- 4}{x^2+ 6x- 40}$ is because you get " $\frac{0}{0}$". And saying that x= 4 makes $x^2+ 6x- 40= 0$ tells you that x- 4 is a factor! Once you know that it should be easy to find the number, a, so that $x^2+ 6x- 40= (x- a)(x- 4)$.