Объяснение:
y = cos(pi+x)/cos(pi/2 + x) = -cos x / (-sin x) = tg x.
y' = (tg x)' = 1/cos²x, y'(-pi/4) = 1/cos²(pi/4) = 1/ (√2/2)² = 1/ (2/4) = 4/2 = 2.
