Given Let lines l and m are two intersecting lines. Again, let n and p be another two lines which are perpendicular to the intersecting lines meet at point D. To prove Two lines n and p intersecting at a point. Proof Suppose we consider lines n and p are not intersecting, then it means they are parallel to each other i.e., n || p …(i) Since, lines n and pare perpendicular to m and l, respectively. But from Eq. (i) n || p it implies that l || m. Hence, it is a contradiction. Thus, our assumption is wrong. Therefore, lines n and p intersect at a point.