One product has the two Br atom on the same side of the ring(cis),and the other has them on opposite sides(trans).We find,however,that only trans-1,2-dibromocyclopentane is produced ;none of the cis product is formed We therefore say that the reaction occurs with anti steriochemistry,meaning that the two bromines have come from opposite side of the molecule one from the top face of thering and one from the bottom face.