A radio station operating at 102.1 MHz broadcasts from two identical antennae at the same elevation but

Question:

A radio station operating at 102.1 MHz broadcasts from two identical antennae at the same elevation but separated by an 8.0-m horizontal distance d, Fig. 24-60. A maximum signal is found along the midline, perpendicular to d at its midpoint and extending horizontally in both directions. If the midline is taken as 0o, at what other angle (s) θ is a maximum signal detected a minimum signal? Assume all measurements are made much farther than 8.0m from the antenna towers.