Given: OD is perpendicular to chord AB of a circle where centre is O. BC is a diameter of the circle.
To Prove: CA = 2OD
Proof: ∵ OD ⊥ AB
∴ D is the mid-point of AB
| The perpendicular drawn from the centre of a circle to a chord bisects the chord.
In ∆BAC,
∵ D is the mid-point of AB and O is the midpoint of BC
OD || AC | By mid-point theorem