y' = e^xcos 3x - 3e^xsin 3x
2) y = ln^2 (x^3 + 1)
y' = 2ln (x^3 + 1)*1/(x^3 + 1)*3x^2
y' = 6x^2*ln (x^3 + 1)/(x^3 + 1)
3) x(t) = 1/3*t^3 + 1/2*t^2 + 1
y(t) = 1/2*t^2 + 1/t
dx/dt = 1/3*3t^2 + 1/2*2t = t^2 + t
dy/dt = 1/2*2t + ln t = t + ln t
y'(x) = dy/dx = (dy/dt) : (dx/dt)
y'(x) = (t^2 + t)/(t + ln t)