Integral of sin(x)*sin(nx) dx

                            //                     2           2               \
                            ||cos(x)*sin(x)   x*cos (x)   x*sin (x)            |
                            ||------------- - --------- - ---------  for n = -1|
                            ||      2             2           2                |
                            ||                                                 |
  /                         ||     2           2                               |
 |                          ||x*cos (x)   x*sin (x)   cos(x)*sin(x)            |
 | sin(x)*sin(n*x) dx = C + |<--------- + --------- - -------------  for n = 1 |
 |                          ||    2           2             2                  |
/                           ||                                                 |
                            || cos(x)*sin(n*x)   n*cos(n*x)*sin(x)             |
                            || --------------- - -----------------   otherwise |
                            ||           2                  2                  |
                            ||     -1 + n             -1 + n                   |
                            \\                                                 /

$$\int \sin{\left(x \right)} \sin{\left(n x \right)}\, dx = C + \begin{cases} - \frac{x \sin^{2}{\left(x \right)}}{2} - \frac{x \cos^{2}{\left(x \right)}}{2} + \frac{\sin{\left(x \right)} \cos{\left(x \right)}}{2} & \text{for}\: n = -1 \\\frac{x \sin^{2}{\left(x \right)}}{2} + \frac{x \cos^{2}{\left(x \right)}}{2} - \frac{\sin{\left(x \right)} \cos{\left(x \right)}}{2} & \text{for}\: n = 1 \\- \frac{n \sin{\left(x \right)} \cos{\left(n x \right)}}{n^{2} - 1} + \frac{\sin{\left(n x \right)} \cos{\left(x \right)}}{n^{2} - 1} & \text{otherwise} \end{cases}$$

Simplify