Recall the interference condition between light waves emitted in phase from two point$-$like sources. Now consider the situation where the sources are half a wavelength out of phase. With reference to the phase equation $=\frac{2}{}(dsin),$ where dsin$$ is the far$-$field path length difference and $$ is the phase difference, write an expression for the constructive and destructive interference conditions. Explain your reasoning in detail.