Math Help - Improper Integral

1. Improper Integral

$\int^3_{-\infty}\frac{dx}{x^2+9}$
I got to the part where $\lim_{b->-\infty}\frac{1}{3}tan^{-1}(1)-\frac{1}{3}tan^{-1}(\frac{b}{3})$
I'm not sure how to evaluate arctan to -infinity...

- Wolfram|Alpha[1%2F(x^2%2B9)%2C[x]]
- Wolfram|Alpha[1%2F%28x^2%2B9%29%2C[x%2C-infinity%2C3]]

2. Originally Posted by WhoCares357
$\int ^3_{-\infty}\frac{dx}{x^2+9)$
I got to the part where $\lim_{b->-\infty}\frac{1}{3}tan^{-1}(1)-\frac{1}{3}tan^{-1}(\frac{b}{3})$
I'm not sure how to evaluate arctan to -infinity...

- Wolfram|Alpha[1%2F(x^2%2B9)%2C[x]]
- Wolfram|Alpha[1%2F%28x^2%2B9%29%2C[x%2C-infinity%2C3]]
familiar with the graph of the arctangent function?

$\lim_{x \to -\infty} \arctan(x) = -\frac{\pi}{2}$

3. Originally Posted by skeeter
familiar with the graph of the arctangent function?

$\lim_{x \to -\infty} \arctan(x) = -\frac{\pi}{2}$
Thanks.