Integral of x*cos(x/2)dx 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 $\operatorname{dv}{\left(x \right)} = \cos{\left(\frac{x}{2} \right)}$.

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

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

   1. Let $u = \frac{x}{2}$.

      Then let $du = \frac{dx}{2}$ and substitute $2 du$:

      $$\int 2 \cos{\left(u \right)}\, du$$

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

         $$\int \cos{\left(u \right)}\, du = 2 \int \cos{\left(u \right)}\, du$$

         1. The integral of cosine is sine:

            $$\int \cos{\left(u \right)}\, du = \sin{\left(u \right)}$$

         So, the result is: $2 \sin{\left(u \right)}$

      Now substitute $u$ back in:

      $$2 \sin{\left(\frac{x}{2} \right)}$$

   Now evaluate the sub-integral.

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

   $$\int 2 \sin{\left(\frac{x}{2} \right)}\, dx = 2 \int \sin{\left(\frac{x}{2} \right)}\, dx$$

   1. Let $u = \frac{x}{2}$.

      Then let $du = \frac{dx}{2}$ and substitute $2 du$:

      $$\int 2 \sin{\left(u \right)}\, du$$

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

         $$\int \sin{\left(u \right)}\, du = 2 \int \sin{\left(u \right)}\, du$$

         1. The integral of sine is negative cosine:

            $$\int \sin{\left(u \right)}\, du = - \cos{\left(u \right)}$$

         So, the result is: $- 2 \cos{\left(u \right)}$

      Now substitute $u$ back in:

      $$- 2 \cos{\left(\frac{x}{2} \right)}$$

   So, the result is: $- 4 \cos{\left(\frac{x}{2} \right)}$

3. Add the constant of integration:

   $$2 x \sin{\left(\frac{x}{2} \right)} + 4 \cos{\left(\frac{x}{2} \right)}+ \mathrm{constant}$$

The answer is:

$$2 x \sin{\left(\frac{x}{2} \right)} + 4 \cos{\left(\frac{x}{2} \right)}+ \mathrm{constant}$$