Question

вычислите ctg(arccos(-4/5)+arcctg(-1)) заранее спаибо!

Answer 1

x = arccos(-4/5) <=> cos x = -4/5 & π/2 ≤ x ≤ π => ctg x = -4/3. 
y = arcctg(-1) <=> ctg y = -1 & 0 < y < π 

ctg(x + y) = (ctg x ctg y - 1)/(ctg x + ctg y) = {(-4/3)(-1) - 1}/(-4/3 - 1) = (1/3)/(-7/3) = -1/7. вроде так