Two complex numbers are represented by c + di.

c + di lies on the 1st Quadrant, which means the polar form of c + di is $re^{i\theta}$, where $r = \sqrt{c^2 + d^2}$, $\theta \in \left(0, \dfrac\pi2\right)$.

e - fi lies on the 4th Quadrant, which means the polar form of e - fi is $Re^{i\phi}$, where $R = \sqrt{e^2 + f^2}$, $\phi \in \left(\dfrac{3\pi}2, 2\pi\right)$

Therefore, (c + di)(e - fi) = $rRe^{i\left(\theta + \phi\right)}$

For $\theta \in \left(0, \dfrac\pi2\right)$ and $\phi \in \left(\dfrac{3\pi}2, 2\pi\right)$, $\theta + \phi \in \left(\dfrac{3\pi}{2} , \dfrac{5\pi}{2}\right)$

Therefore (c + di)(e - fi) can lie inside the 4th Quadrant and the 1st Quadrant.