Prove that the straight lines perpendicular to the same straight line are parallel to one another.
Let AB and CD perpendicular to the line MN
∠ABD = 90o(Since, AB perpendicular MN) (i)
∠CON = 90o(Since, CD perpendicular MN) (ii)
Now,
∠ABD = ∠CON = 90o
Therefore,
AB ‖ CD (Since, corresponding angles are equal)