Question

Дано: ctg x=3/4 ; ctg y=1/7 . Найти x+y

Answer 1

$ctg(x+y)= \dfrac{ctgx*ctgy-1}{ctgx+ctgy} =\dfrac{ \frac{3}{4} * \frac{1}{7} -1}{ \frac{3}{4}+ \frac{1}{7}} =(- \frac{25}{28}) : \frac{25}{28} =-1$
=> x+y = 135° или х+у = 315°