Two towers of a radio station are 4.00 X 102 m apart along an east-west line. The towers act essentially as point sources, radiating in phase at a frequency of 1.00 x 106 Hz. Radio waves travel at 3.00 x 108 m/s. (a) In which directions is the intensity of the radio signal at a maximum for listeners 20.0 km north of the trans- mitter (but not necessarily directly north of it)? (b) In which directions would you find the intensity at a minimum, north of the transmitter, if the towers were to start transmitting in opposite phase?