(c)
Here, $\tan{\frac{P}{2} + \tan{\frac{\mathcal{Q}}{2} = - \frac{b}{a}}}$
And $\tan{\frac{P}{2}\tan{\frac{\mathcal{Q}}{2} = \frac{c}{a}}\ \ \ \ \ \ \ \ldots(i)}$
Also, $\frac{P}{2} + \frac{\mathcal{Q}}{2} + \frac{R}{2} = \frac{\pi}{2}\ \ \ \ \ \ \lbrack\because P + \mathcal{Q +}R = \pi\rbrack$
$\Rightarrow \frac{P + \mathcal{Q}}{2} = \frac{\pi}{4}\ \ \ \ \ \ \left\lbrack \because\angle R = \frac{\pi}{2},\ given \right\rbrack$
$\tan\left( \frac{P}{2} + \frac{\mathcal{Q}}{2} \right) = 1 \Rightarrow \frac{\tan{\frac{P}{2} + \tan\frac{\mathcal{Q}}{2}}}{1 - \tan{\frac{P}{2}\tan\frac{\mathcal{Q}}{2}}} = 1$
$\Rightarrow \frac{- \frac{b}{a}}{1 - \frac{c}{a}} = 1\ \ \Rightarrow \ \ - \frac{b}{a} = 1 - \frac{c}{a}$ [from Eq. (i)]
$\Rightarrow c = a + b$