Write the condition of destructive interference in terms of path and phase difference.

(N/A) For destructive interference to occur, the waves must arrive at a point in opposite phase.
$1$. Phase difference $(\Delta \phi)$: The phase difference must be an odd multiple of $\pi$. Mathematically, $\Delta \phi = (2n + 1)\pi$, where $n = 0, 1, 2, 3, \dots$.
$2$. Path difference $(\Delta x)$: Since the relation between path difference and phase difference is $\Delta \phi = \frac{2\pi}{\lambda} \Delta x$, we substitute the condition for destructive interference:
$(2n + 1)\pi = \frac{2\pi}{\lambda} \Delta x$
$\Delta x = (2n + 1) \frac{\lambda}{2}$, where $n = 0, 1, 2, 3, \dots$.