Let $f(x) = \sqrt{1+ \cos 2x}$ , $x \in(\frac{\pi}{2},\pi]$ , where $\cos$ is negative.
On solving , $f(x)$ comes out to be $\sqrt{\cos²x}$. Now its result can be $+/- \cos x$ , $\cos x$ being $-ve$ and $-\cos x$ being $+ve$ . In both the cases the original function remains valid . But on graphing it online the plotted graph only shows the positive value of $\cos x $
(Ignore the other functions )
Why is it happening ?