Three particles start from the origin at the same time, one with a velocity 𝑣1 along 𝑥-axis, the second along the 𝑦-axis with a velocity 𝑣2 and the third along 𝑥 = 𝑦 line. The velocity of the third so that the three may always lie on the same line is

Question : Three particles start from the origin at the same time, one with a velocity 𝑣1 along 𝑥-axis, the second along the 𝑦-axis with a velocity 𝑣2 and the third along 𝑥 = 𝑦 line. The velocity of the third so that the three may always lie on the same line is