sin(x + y) = cosx lnydsin(x + y)/d(x + y) · d(x + y)/dx = lny d(cosx)/dx + cosx d(lny)/dy · dy/dxcos(x + y) · (1 + dy/dx) = lny · (- sinx) + cosx · 1/y · dy/dxcos(x + y) + cos(x + y) dy/dx = - s...