Question
Prove that tangents drawn at the ends of a diameter of a circle are parallel to each other.
Solution
Let AB be the diameter of a circle, with centre O. The tangents PQ and RS are drawn at points A and B, respectively.
We know that a tangent at any point of a circle is perpendicular to the radius through the point of contact.
∴ OA ⊥ PQ and OB ⊥ RS
⇒ ∠OBR = 90°
∠OBS = 90°
∠OAP = 90°
∠OAQ = 90°
We can observe the following:
∠OBR = ∠OAQ and ∠OBS = ∠OAP
Also, these are the pair of alternate interior angles.
Since alternate interior angles are equal, the lines PQ and RS are parallel to each other.
Hence, proved.
