(a)
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Required area
$= \int_{0}^{x/4}{(\cos{x - \sin{x)dx + \int_{\pi/4}^{5\pi/4}{(\sin{x - \cos{x)dx + \int_{5\pi/4}^{3\pi/2}{(\cos{x - \sin{x)dx}}}}}}}}}$
$= (\sin{x + \cos{x)_{0}^{\pi/4} + ( - \cos{x - \sin{x)_{\pi/4}^{5\pi/4} + (\sin{x + \cos{x)_{5\pi/4}^{3\pi/2}}}}}}}$
$= \left( 4\sqrt{2} - 2 \right)sq\ units$