i assumed two functions y1 = Asin(wt+phi1) and similarly y2
y1=A= A sinphi1 , this gives phi1= pi/2
similarly phi2 can be 7pi/6 or 11pi/6
since velocities are opposite and that of y1 is +ve , vel of y2 must be -ve so phi2= 7pi/6
now we have complete functions of y1 nd y2 . equate them
edit: i have solved this but looking for better ways to approach this problem
i just did some tiny error in taking initial phase