Question

ctg(п/7)+ctg(3п/4)+ctg(6п/7)

Answer 1

$ctgfrac{pi}{7}+ctgfrac{3pi}{4}+ctgfrac{6pi}{7}=ctgfrac{pi}{7}+ctg(pi-frac{pi}{4})+ctg(pi-frac{pi}{7})=\ctgfrac{pi}{7}-ctgfrac{pi}{4}-ctgfrac{pi}{7}=-ctgfrac{pi}{4}=-1.$