Prove that the tangents drawn at the ends of a diameter of a circle are parallel.
Prove that tangents drawn at the ends of a diameter of a circle are parallel to each other.
Given: CD and EF are the tangents at the end points A and B of the diameter AB of a circle with centre O.
To prove: CD || EF.
Proof: CD is the tangent to the circle at the point A.
∴ ∠BAD = 90°
EF is the tangent to the circle at the point B.
∴ ∠ABE = 90°
Thus, ∠BAD = ∠ABE (each equal to 90°).
But these are alternate interior angles.
∴ CD || EF
Let AB be a diameter of the circle. Two tangents PQ and RS are drawn at points A and B respectively.
Radius drawn to these tangents will be perpendicular to the tangents.
Thus, OA ⊥ RS and OB ⊥ PQ
∠OAR = 90º
∠OAS = 90º
∠OBP = 90º
∠OBQ = 90º
It can be observed that
∠OAR = ∠OBQ (Alternate interior angles)
∠OAS = ∠OBP (Alternate interior angles)
Since alternate interior angles are equal, lines PQ and RS will be parallel.