Waves are created on the water surface with the help of two springs, which are separated by 20 cm. The wave sources oscillate at a frequency of 3 Hz, but not in the same phase. The wave caused by the first source leads the second by a quarter of a wavelength. Observing the interference of the two waves far from the source, at what angles, relative to the bisector between the two sources, do the waves add up (interfere constructively)? The speed of the waves is 0.4 m/s.
