1. The problem statement, all variables and given/known data Two speakers A and B, sends out sounds at 400 hz In what distance x between speaker A and the point P is it constructive interference ? http://s716.photobucket.com/user/Pitoraq/media/Fys2121_zps9a68fef2.png.html 2. Relevant equations λ = 2ΔL/(2p-1), v = 340 m/s f = 400 Hz 3. The attempt at a solution λ = 2ΔL/(2p-1), λ = 340/400 = 0.85 m <==> lowest constructive interference p = 1 0.85 m = ΔL <==> 0.85 = y - x, where y = (2.5)^2+x^2=y^2 is the distance between P and B. Is this right ?