Two particles, 1 and 2, move with constant velocities v₁ and v₂. At the initial moment their radius vectors are equal to r₁ and r₂. The relation between these four vectors for the particles to collide is (→r₁− →r₂) |→r₁− →r₂|= x (→v₂− →v₁)/|→v₂− →v₁ |. Find x.