During wich two time intervals does the particle undergo equal displacement

Basically, you want to take the integral of each interval and compare them. The two intervals with the same integral represent equal displacement of the particle. And since delta(x) is always 2, all you have to do is average the initial and final velocities of each interval and multiply by two to find total displacement.

Hope it helped.

Edit to show calculations:

2 * [ (0 + 10)/2 ] = 10 for interval AB
2 * [ (7 + 3)/2 ] = 10 for interval DE

4. 50x10= 500m/s 5. 52m/s

3is a crest4 is a trough 2 is the amplitude 1 is the wavelength