(a) $x = 3\sin{2t + 4\cos{2t.}}$ From given equation $a_{1} = 3,a_{2} = 4\ $and $\phi = \frac{\pi}{2}$ $\therefore a = \sqrt{a_{1}^{2} + a_{2}^{2}} = \sqrt{3^{2} + 4^{2}} = 5 \Rightarrow v_{\max} = a\omega = 5 \times 2 = 10$
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Ph.D. in Physics with 19+ years of teaching experience.