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In the following figure, point O is the centre of the circle and length of chord AB is equal to the radius of the circle. Find the measures of :(i) ∠AOB(ii) arc AB(iii) ∠ACB[Figure: circle with centre O; chord AB below the centre, C on the major arc…

Q.3 (A)(2) In the following figure, point O is the centre of the circle and length of chord AB is equal to the radius of the circle. Find the measures of :

(i) ∠AOB
(ii) arc AB
(iii) ∠ACB

[Figure: circle with centre O; chord AB below the centre, C on the major arc AB above the centre; seg OA, seg OB, seg CA and seg CB drawn.]

by completing the activity.

Activity :

In \(\Delta AOB\),

AO = OB = AB

\(\therefore \Delta AOB\) is an ____ triangle.

\(\therefore m\angle AOB = ____\)

\(m\angle AOB = m(\text{arc AB}) = ____\) ......... (definition of measure of an arc)

\(m\angle ACB = \dfrac{1}{2} \times ____\) ......... (inscribed angle theorem)

\(= \dfrac{1}{2} \times 60^\circ\)

\(m\angle ACB = ____\)

1 answer

Best answer

Answer: (i) m∠AOB = 60º, (ii) m(arc AB) = 60º, (iii) m∠ACB = 30º. The blanks are equilateral, 60º, 60º, m(arc AB) and 30º.

The blanks: Δ AOB is an equilateral triangle (all three sides equal the radius), so m∠AOB = 60º; the measure of an arc equals the measure of its central angle, so m(arc AB) = 60º.

The inscribed angle is half the arc it intercepts: m∠ACB = \(\dfrac{1}{2}\) × m(arc AB) = \(\dfrac{1}{2}\) × 60º = 30º.

Doubtly AI · 25 Oct 2026 AI-verified · Oct 2026 Report
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