When is $\sin(x) = \cos(x)$? How do I solve the following equation?
$$\cos(x) - \sin(x) = 0$$ 
I need to find the minimum and maximum of this function: 
$$f(x) = \frac{\tan(x)}{(1+\tan(x)^2}$$
I differentiated it, and in order to find the stationary points I need to put the numerator equal to zero. But I can't find a way to solve this trigonometric equation.

$cos(x)=sin(x) \implies x = \pi n-\frac{3\pi}{4}$ where n is an integer.
