Originally Posted by

**javax** Hullo.

The function I was trying to draw was $\displaystyle f(x) = \frac{5-x}{9-x^2}$

The first derivative is $\displaystyle f'(x) = \frac{-x^2+10x-9}{(9-x^2)^2}$

When I come to determine Concave Up & Concave Down intervals...I calculate $\displaystyle f''(x)$ which is $\displaystyle f''(x) = \frac{-2(x^3-15x^2+27x-45)}{(9-x^2)^3}$

The problem now is that I can't find zeros of this equation, neither simplify anymore! I know there are rules to solve these but they take time I think! I had this function on test! There wasn't much time to calculate...!

So if you know any shorter way...tell me, I'd appreciate!