Integral of sin5xcosx dx

1. Rewrite the integrand:

   $$\sin{\left(5 x \right)} \cos{\left(x \right)} = 16 \sin^{5}{\left(x \right)} \cos{\left(x \right)} - 20 \sin^{3}{\left(x \right)} \cos{\left(x \right)} + 5 \sin{\left(x \right)} \cos{\left(x \right)}$$

2. Integrate term-by-term:

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

      $$\int 16 \sin^{5}{\left(x \right)} \cos{\left(x \right)}\, dx = 16 \int \sin^{5}{\left(x \right)} \cos{\left(x \right)}\, dx$$

      1. There are multiple ways to do this integral.

         Method #1

         1. Let $u = \sin{\left(x \right)}$.

            Then let $du = \cos{\left(x \right)} dx$ and substitute $du$:

            $$\int u^{5}\, du$$

            1. The integral of $u^{n}$ is $\frac{u^{n + 1}}{n + 1}$ when $n \neq -1$:

               $$\int u^{5}\, du = \frac{u^{6}}{6}$$

            Now substitute $u$ back in:

            $$\frac{\sin^{6}{\left(x \right)}}{6}$$

         Method #2

         1. Rewrite the integrand:

            $$\sin^{5}{\left(x \right)} \cos{\left(x \right)} = \left(1 - \cos^{2}{\left(x \right)}\right)^{2} \sin{\left(x \right)} \cos{\left(x \right)}$$

         2. Let $u = 1 - \cos^{2}{\left(x \right)}$.

            Then let $du = 2 \sin{\left(x \right)} \cos{\left(x \right)} dx$ and substitute $\frac{du}{2}$:

            $$\int \frac{u^{2}}{4}\, du$$

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

               $$\int \frac{u^{2}}{2}\, du = \frac{\int u^{2}\, du}{2}$$

               1. The integral of $u^{n}$ is $\frac{u^{n + 1}}{n + 1}$ when $n \neq -1$:

                  $$\int u^{2}\, du = \frac{u^{3}}{3}$$

               So, the result is: $\frac{u^{3}}{6}$

            Now substitute $u$ back in:

            $$\frac{\left(1 - \cos^{2}{\left(x \right)}\right)^{3}}{6}$$

      So, the result is: $\frac{8 \sin^{6}{\left(x \right)}}{3}$

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

      $$\int \left(- 20 \sin^{3}{\left(x \right)} \cos{\left(x \right)}\right)\, dx = - 20 \int \sin^{3}{\left(x \right)} \cos{\left(x \right)}\, dx$$

      1. Let $u = \sin{\left(x \right)}$.

         Then let $du = \cos{\left(x \right)} dx$ and substitute $du$:

         $$\int u^{3}\, du$$

         1. The integral of $u^{n}$ is $\frac{u^{n + 1}}{n + 1}$ when $n \neq -1$:

            $$\int u^{3}\, du = \frac{u^{4}}{4}$$

         Now substitute $u$ back in:

         $$\frac{\sin^{4}{\left(x \right)}}{4}$$

      So, the result is: $- 5 \sin^{4}{\left(x \right)}$

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

      $$\int 5 \sin{\left(x \right)} \cos{\left(x \right)}\, dx = 5 \int \sin{\left(x \right)} \cos{\left(x \right)}\, dx$$

      1. Let $u = \cos{\left(x \right)}$.

         Then let $du = - \sin{\left(x \right)} dx$ and substitute $- du$:

         $$\int u\, du$$

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

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

            1. The integral of $u^{n}$ is $\frac{u^{n + 1}}{n + 1}$ when $n \neq -1$:

               $$\int u\, du = \frac{u^{2}}{2}$$

            So, the result is: $- \frac{u^{2}}{2}$

         Now substitute $u$ back in:

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

      So, the result is: $- \frac{5 \cos^{2}{\left(x \right)}}{2}$

   The result is: $\frac{8 \sin^{6}{\left(x \right)}}{3} - 5 \sin^{4}{\left(x \right)} - \frac{5 \cos^{2}{\left(x \right)}}{2}$

3. Add the constant of integration:

   $$\frac{8 \sin^{6}{\left(x \right)}}{3} - 5 \sin^{4}{\left(x \right)} - \frac{5 \cos^{2}{\left(x \right)}}{2}+ \mathrm{constant}$$

The answer is:

$$\frac{8 \sin^{6}{\left(x \right)}}{3} - 5 \sin^{4}{\left(x \right)} - \frac{5 \cos^{2}{\left(x \right)}}{2}+ \mathrm{constant}$$