(a)
The points of intersection of given curves are (0,0) and
$\left( \frac{1}{a},\frac{1}{a} \right)$
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$\therefore\ \ Required\ area\ OABCO = area\ of\ OCBDO - area\ of\ OABDO$
$\Longrightarrow \ \ \int_{0}^{1/a}{\left( \sqrt{\frac{x}{a}} - {ax}^{2} \right)dx = 1}\ \ \ \lbrack given\rbrack$
$\Longrightarrow \ \ \left( \frac{1}{\sqrt{a}} \bullet \frac{x^{3/2}}{3/2} - \frac{{ax}^{3}}{3} \right)_{0}^{1/a} = 1$
$\Longrightarrow \ \frac{2}{{3a}^{2}} - \frac{1}{{3a}^{2}} = 1$
$\Longrightarrow \ \ a^{2} = \frac{1}{3}\ \Longrightarrow a = \frac{1}{\sqrt{3}}\ \ \ \ \ \ \ \ \lbrack as\ a > 0\rbrack$