1. The problem statement, all variables and given/known data Two coherent sources of radio waves, A and B, are 5.00 meters apart. Each source emits waves with wavelength 6.00 meters. Consider points along the line connecting the two sources. At what distance from source A is there constructive interference between points A and B? 2. Relevant equations Let P be the point of constructive interference: [tex]r_1 - r_2 = m\lambda [/tex] where [tex]r_1 [/tex] is the distance from A to P and [tex]r_2[/tex] is the distance from P to B. These were the hints given, and don't make sense. 3. The attempt at a solution I got the answer of 2.5 metres by drawing a diagram and estimating where the two waves would cross (constructive interference). The answer was correct, a lucky guess... I don't know how to apply that equation. Does it need to be applied twice? For m I would use the value of 1?