I feel so silly right now, because this problem is the 1st problem of my physics problem set(and easiest), and I've done all the rest of the harder problems, but I can't get this simple problem! 1. The problem statement, all variables and given/known data two in phase sources of waves are separated by a distance of 4.00m these sources produce identical waves that have a wave length of 5.00 m. on the line between them there are two places at which the same type of interference occurs. a) is it constructive or destructive interference and b) where are the places located 2. Relevant equations l2-l1= m lambda (wavelength) l2-l1= (m+1/2) lambda 3. The attempt at a solution l2-l1= 4 meters lambda = 5 meters m= 0.80 meters I'm so lost.