I=∫02π[sin2x(1+cos3x)]dx…(1)
I=∫02π[sin(2π−2x)(1+cos(2π−3x))]dx
Applying (∫0af(x)=∫0af(a−x)dx)
I=∫02π[−sin2x(1+cos3x)]dx…(2)
Adding (1) and (2)
2I=∫02π([sin2x(1+cos3x)]+[−sin2x(1+cos3x)])dx
\Rightarrow 2I=\int _{0}^{2\pi }-1dx {\because [x]+[-x]={\begin{matrix}0 :x\in I \\ -1 :x\notin I\end{matrix}
⇒2I=(−x)02π
⇒2I=−2π
⇒I=−π