(a) $\sin{x > \sin^{3}x}$ $\Rightarrow \ \int_{0}^{\pi/2}{\sin{x\ dx > \int_{0}^{\pi/2}{\sin^{3}{x\ dx}}}}$ $\Rightarrow \ I_{1} > I_{2}$
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Ph.D. in Physics with 19+ years of teaching experience.