Производные 1 порядка:
dz / dx = 1 / tg(x/y) * 1/ (cos(x/y))^2 * 1/y = 1 / (y * tg(x/y) * (cos(x/y))^2) = 1 / (y * sin(x/y) * cos(x/y)) = 2 / (y * sin (2x/y)) = 2/y * 1/sin (2x/y)
dz / dy = 1 / tg(x/y) * 1/ (cos(x/y))^2 * (- x/y^2) = - 2x / (y^2 * sin (2x/y)) = -2x/y^2 * 1/sin (2x/y)