Interference of two radio waves

[username12345]

Homework Statement

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?

Homework Equations

Let P be the point of constructive interference:

$$r_1 - r_2 = m\lambda$$ where $$r_1$$ is the distance from A to P and $$r_2$$ is the distance from P to B.

These were the hints given, and don't make sense.

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?

 

[Redbelly98]

m could be any integer, not just 1.

Try m = 0 or 1, and see what you can come up using your equation,

r₁ - r₂ = m λ​