Integral of (4-x)*cosxdx dx

1. There are multiple ways to do this integral.

   Method #1

   1. Let $u = - x$.

      Then let $du = - dx$ and substitute $du$:

      $$\int \left(- u \cos{\left(u \right)} - 4 \cos{\left(u \right)}\right)\, du$$

      1. Integrate term-by-term:

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

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

            1. Use integration by parts:

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

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

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

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

               1. The integral of cosine is sine:

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

               Now evaluate the sub-integral.

            2. The integral of sine is negative cosine:

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

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

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

            $$\int \left(- 4 \cos{\left(u \right)}\right)\, du = - 4 \int \cos{\left(u \right)}\, du$$

            1. The integral of cosine is sine:

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

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

         The result is: $- u \sin{\left(u \right)} - 4 \sin{\left(u \right)} - \cos{\left(u \right)}$

      Now substitute $u$ back in:

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

   Method #2

   1. Rewrite the integrand:

      $$\left(4 - x\right) \cos{\left(x \right)} = - x \cos{\left(x \right)} + 4 \cos{\left(x \right)}$$

   2. Integrate term-by-term:

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

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

         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 $\operatorname{dv}{\left(x \right)} = \cos{\left(x \right)}$.

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

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

            1. The integral of cosine is sine:

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

            Now evaluate the sub-integral.

         2. The integral of sine is negative cosine:

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

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

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

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

         1. The integral of cosine is sine:

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

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

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

   Method #3

   1. Use integration by parts:

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

      Let $u{\left(x \right)} = 4 - x$ and let $\operatorname{dv}{\left(x \right)} = \cos{\left(x \right)}$.

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

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

      1. The integral of cosine is sine:

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

      Now evaluate the sub-integral.

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

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

      1. The integral of sine is negative cosine:

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

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

2. Add the constant of integration:

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

The answer is:

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