Integral X Sin Cos D10405
1. **Problem statement:** Find the integral $$\int x \sin(x) \cos(x) \, dx$$.
2. **Formula and identities:** Use the double-angle identity for sine: $$\sin(2x) = 2 \sin(x) \cos(x)$$, so $$\sin(x) \cos(x) = \frac{\sin(2x)}{2}$$.
3. **Rewrite the integral:**
$$\int x \sin(x) \cos(x) \, dx = \int x \frac{\sin(2x)}{2} \, dx = \frac{1}{2} \int x \sin(2x) \, dx$$.
4. **Integration by parts:** Let
- $$u = x \implies du = dx$$
- $$dv = \sin(2x) dx \implies v = -\frac{\cos(2x)}{2}$$
5. **Apply integration by parts formula:**
$$\int u \, dv = uv - \int v \, du$$
So,
$$\frac{1}{2} \int x \sin(2x) \, dx = \frac{1}{2} \left( -\frac{x \cos(2x)}{2} + \int \frac{\cos(2x)}{2} \, dx \right) = -\frac{x \cos(2x)}{4} + \frac{1}{4} \int \cos(2x) \, dx$$.
6. **Integrate $$\int \cos(2x) dx$$:**
$$\int \cos(2x) \, dx = \frac{\sin(2x)}{2} + C$$.
7. **Substitute back:**
$$-\frac{x \cos(2x)}{4} + \frac{1}{4} \cdot \frac{\sin(2x)}{2} + C = -\frac{x \cos(2x)}{4} + \frac{\sin(2x)}{8} + C$$.
**Final answer:** $$\boxed{-\frac{x}{4} \cos(2x) + \frac{1}{8} \sin(2x) + C}$$.
This matches option (c).