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**AZach** $\displaystyle \lim_{x \to 5}\frac{x^2-10x+25}{x^4-625}$

First step I did all the factor: $\displaystyle \lim_{x \to 5}\frac{(x-5)(x-5)}{(x^2+25)(x^2-25)}$

-And then factoring the denominator again I got: $\displaystyle \lim_{x \to 5}\frac{(x-5)(x-5)}{(x^2+25)(x+5)(x-5)}$ ; but I have a question here, and I think it's just because I'm really tired, but can I factor $\displaystyle (x^2+25)$? I keep thinking $\displaystyle (a^2+b^2)$ but my brain's not working.

-Anyway, I cancelled the $\displaystyle (x-5)$ from the numerator / denominator and then evaluated the limit using direct substitution and I got zero. My book says that's wrong though. If anyone has a chance to throw me a tip for these two questions I'd really appreciate it!