1
Substitute \( u = 3x \), \( du = 3dx \) ⇒ \( dx = \frac{du}{3} \)
2
Change limits: when x=0, u=0; when x=π/6, u=π/2
3
Rewrite integral:
\[ \frac{1}{3} \int_{0}^{\frac{\pi}{2}} \sin^5 u \, du \]
4
Express sin⁵u as sinu(1-cos²u)²:
\[ \sin^5 u = \sin u (1 - 2\cos^2 u + \cos^4 u) \]
5
Let \( v = \cos u \), \( dv = -\sin u du \)
6
Transform integral:
\[ -\frac{1}{3} \int (1 - 2v^2 + v^4) dv \] from v=1 to v=0
7
Integrate term by term:
\[ -\frac{1}{3} \left[ v - \frac{2}{3}v^3 + \frac{1}{5}v^5 \right]_1^0 \]
8
Evaluate:
\[ -\frac{1}{3} \left[ 0 - \left(1 - \frac{2}{3} + \frac{1}{5}\right) \right] = \frac{1}{3} \left(1 - \frac{2}{3} + \frac{1}{5}\right) = \frac{8}{45} \]
Final Answer: \[ \frac{8}{45} \]