Вычислите ctg(arccos(-4/5)+ arcctg(-1))

X=arccos(-4?5)<=>cos x=-4/5 π/2≤x≤ π=> ctg=-4/3.
y=arcctg(-1)<=>ctg y--1 & 0<y< π
ctg(x+y)=(ctg x-1)/(ctg x+ ctg y)={(-4/3)(-1)-1}/(-4/3-1)=(1/3)/(-7/3)=-1/7