Originally Posted by

**Mathlv** Hello,

I am doing a trigonometric derivative problem, but I think I have forgotten the right step of when to add a $\displaystyle \pi n$ or when to add a 2$\displaystyle \pi n$. For example in my book, one of the problem says Cosx = $\displaystyle

\frac{{ - 1}}{2}

$ $\displaystyle

\Rightarrow

$ x = $\displaystyle

2\frac{\pi }{3} + 2\pi n

$ or $\displaystyle

4\frac{\pi }{3} + 2\pi n

$. Now at other problem I see it says tanx = 1 $\displaystyle

\Rightarrow

$ x = $\displaystyle

\frac{\pi }{4} + \pi n

$ (n is an integer). Thank you for the help.