The derivative of the product of the two functions is equal to the product of the second function and the derivative of the first function plus the product of the first function and the derivative of the second function.
i.e. if, u and be two differentiable functions of x, then
d/dx (uv) = v d/dx (u) + u d/dx (v)
Note. The above formula can be extended to the product of more than two functions. For example if y = uvw, a product of three differentiable functions of x, then