Two particles are projected simultaneously in the same vertical plane from the same point, with

Two particles are projected simultaneously in the same vertical plane from the same point, with different speeds `u_(1)` and `u_(2)`, making angles `theta_(1)` and `theta_(2)` respectively with the horizontal, such that `u_(1) cos theta_(1) = u_(2) cos theta_(2)`. The path followed by one, as seen by the other (as long as both are in flight), is