Integral of 4xsinx dx

1. The integral of a constant times a function is the constant times the integral of the function:

   $$\int 4 x \sin{\left(x \right)}\, dx = 4 \int x \sin{\left(x \right)}\, dx$$

   1. Use integration by parts:

      $$\int \operatorname{u} \operatorname{dv} = \operatorname{u}\operatorname{v} - \int \operatorname{v} \operatorname{du}$$

      Let $u{\left(x \right)} = x$ and let $\operatorname{dv}{\left(x \right)} = \sin{\left(x \right)}$.

      Then $\operatorname{du}{\left(x \right)} = 1$.

      To find $v{\left(x \right)}$:

      1. The integral of sine is negative cosine:

         $$\int \sin{\left(x \right)}\, dx = - \cos{\left(x \right)}$$

      Now evaluate the sub-integral.

   2. The integral of a constant times a function is the constant times the integral of the function:

      $$\int \left(- \cos{\left(x \right)}\right)\, dx = - \int \cos{\left(x \right)}\, dx$$

      1. The integral of cosine is sine:

         $$\int \cos{\left(x \right)}\, dx = \sin{\left(x \right)}$$

      So, the result is: $- \sin{\left(x \right)}$

   So, the result is: $- 4 x \cos{\left(x \right)} + 4 \sin{\left(x \right)}$

2. Add the constant of integration:

   $$- 4 x \cos{\left(x \right)} + 4 \sin{\left(x \right)}+ \mathrm{constant}$$

The answer is:

$$- 4 x \cos{\left(x \right)} + 4 \sin{\left(x \right)}+ \mathrm{constant}$$