(d)
Given, $\tan{\left( \frac{\alpha\pi}{4} \right) = \tan\left( \frac{\pi}{2} - \frac{\beta\pi}{4} \right)}$
$\Rightarrow \ \ \frac{\alpha\pi}{4} = n\pi + \frac{\pi}{2} - \frac{\beta\pi}{4}$
$\Rightarrow \ \ (\alpha + \beta)\frac{\pi}{4} = \left( \frac{2n + 1}{2} \right)\pi$
$\Rightarrow \ \ \ \ \alpha + \beta = 2(2n + 1),\ \forall\ n \in I$