Differentiate cos(2x^3)/3x

Using quotient rule y = u/v - dy/dx = (v.du/dx - u.dv/dx)/v².u = cos(2x³) , a = 2x³. du/da = -sin(a), da/dx = 6x². From chain rule, we know that du/dx = du/da . da/dx, so du/dx = -6x²sin(2x³). We know that dv/dx = 3. We now have all the necessary terms to configure dy/dx: dy/dx =( 3x . -6x²sin(2x³)-3cos(2x³))/9x² = (-18x³sin(2x³) - 3cos(2x³))/9x²