Following figure shows sources S₁ and S₂ that emits light of wavelength λ in all directions. The sources are exactly in phase and are separated by a distance equal to 1.5λ. If we start at the indicated start point and travel along path 1 and 2, the interference produce a maxima all along

Path 1

At any point along the path 1, path difference between the waves is 0. 

Hence maxima is obtained all along the path 1.

At any point along the path 2, path difference is 1.5λ which is odd multiple of $\frac{λ}{2}$, so minima is obtained all along the path 2.