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WBBSEClass 10MathematicsTheorem Related To Angle In A Circle03 Mark2025 Easy

QQuestion

O is the circumcentre of the triangle ABC. OD ⊥ BC. Prove that ∠BOD = ∠BAC.

Exam-ready answer • 03 Mark

Answer

Given: O is the circumcentre of triangle ABC. OD is perpendicular to BC.

To Prove: ∠BOD = ∠BAC

Proof:

O is the circumcentre, so it is equidistant from A, B, and C.

OD is perpendicular to BC, so it bisects the arc BC that does not contain A.

The angle subtended by the same arc at the centre is twice the angle subtended at the circumference.

Thus,

∠BOD = 2 ∠BCA

∠BAC = 2 ∠BCA

So, ∠BOD = ∠BAC   (Hence proved)

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