A point Q lies on a straight line m.
a. (i) Draw a straight line n passing through Q and forming a right angle with m. Give a logical explanation for the existence of such a line.
b. (ii) Prove that no other straight line distinct from n and passing through Q can be perpendicular to m.
c. (iii) Hence, show that exactly one perpendicular can be drawn to a given line at a point lying on it.