How Do Antenna Positions Affect Radio Wave Interference?

[Punkyc7]

Two radio antennas A and B radiate in phase. Antenna B is a distance of 130 m to the right of antenna A. Consider point Q along the extension of the line connecting the antennas, a horizontal distance of 50.0 m to the right of antenna B. The frequency, and hence the wavelength, of the emitted waves can be varied.

What is the longest wave length that cause constructive interference and what is the longest wavelength that cause destructive interference

r1-r2=(.5+m)\lambda
r1-r2=(m)\lambda

After a drew my picture I got r1 =180 and r2=50
then I plugged into the formulas

130=.5\lambda destructive=260
130=\lambda constructive

Is that right because the problem seems to easy?

 

[ehild]

It is that easy but do not forget to add the unit of wavelength to your result.

ehild