The solution of problem 3.17 cr 3 of Prokofiev´s proble

The solution of problem 3.17 cr 3 of Prokofiev´s proble

Task 3.17
The oscillating points are removed from the source of oscillations by a distance of 0.5 and 1.77 m in the direction
Wave propagation. The phase difference of their oscillations is equal to 3/4. The oscillation frequency of the source is 100 s -1.
Determine the wavelength and the speed of its propagation.