When two straight lines intersects at a point and forms a linear pair of equal angles, then they are perpendicular.
Perpendicular Lines Theorem
If two lines are perpendicular, then they intersect to form four right angles. If one angle is a right angle, then the other three are also right angles.
Perpendicular Transversal Theorem
In a plane, if a line is parallel to another line and is perpendicular, then the other line is also perpendicular.
