$arctan(-1)=a\rightarrow tana=-1\rightarrow a=-\frac{\pi}{4}$,
$arcsin(\frac 12)=b\rightarrow sinb=\frac 12\rightarrow b=\frac{\pi}{6}$,
$arccos(\frac{-\sqrt 3}{2})=c\rightarrow cosc=\frac{-\sqrt 3}{2}\rightarrow c=\frac{5\pi}{6}$, Buradan $a+b+c=\frac{3\pi}{4}$ bulunur.