Question

Two sinussoidal waves identical except for phase travel in the same direction along a string and interfere to produce a resultant wave given by y(x,t)= (3.0mm) sin(20 rad/m)x - 4.0rad/s t + 0.820 rad) with x in meters and t in seconds. What is a) the wavelength of the two waves b) the phase difference between them c) their amplitude

Work:
I know the resultant of the waves comes from the formula
y(x,t)=y(x,t) + y2(x,t)
since there out of phase
y(x,t)= {2Ycos1/2phase}sin(kx-wt + 1/2phase)
I tried to figure out the equations but I am lost. I read the book and its confusing more on this section.Help is appreciated. Thank you :)

Well, you almost have it.
y(x,t)= {2Ycos1/2phase}sin(kx-wt+1/2phase)
3mm= 2Ycos1/2phase
and 1/2 phase= .820radians.
Solve for phase, then Y.

you know k= 20, and w=4
solve for w, and if you wish, k. k ought to related to wavelength. Finally, knowing w, you have f.