(d)
Required area
= area of rectangle $OABC -$ area of curve $OBCO$
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$= \frac{\pi}{4\sqrt{2}} - \int_{0}^{\frac{\pi}{4}}{\sin{y\ dy}}$
$= \frac{\pi}{4\sqrt{2}} + \lbrack\cos{y\rbrack_{0}^{\frac{\pi}{4}}}$
$= \left\lbrack \frac{\pi}{4\sqrt{2}} + \left( \frac{1}{\sqrt{2}} - 1 \right) \right\rbrack\ sq\ unit$