a. For $\frac{\pi}{2} \leq x \leq \frac{3\pi}{2}$, the curve is above the x-axis. So the area is given by:
$$\text{Area} = \int_{\frac{\pi}{2}}^{\frac{3\pi}{2}} |x \cos x| dx$$
b. For $\frac{3\pi}{2} \leq x \leq \frac{5\pi}{2}$, the curve is below the x-axis.
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