In the case the double slits δ=h-K≈dsin8 D>a is very small s08=g9-d月 疗=k=02) Constructive bright fringes 号=-&-123) Destructive dark fringesIn the case the double slits： r1 r2   x P S s1 s2 D d o P S s1 s2 D d o Constructive bright fringes Destructive dark fringes