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.