Find dy/dx when y = x^2(cos(x)).

y = x²(cos(x)) therefore we will need to use the product rule, 

dy/dx = u dv/dx + v du/dx

where u = x² and v = cos(x)

du/dx = 2x and dv/dx = - sin(x), (don't forget the negative symbol when differentiating cosine)

dy/dx = x²(- sin(x)) + cos(x)(2x)

dy/dx = 2x(cos(x)) - x²(sin(x))