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In the given figure, O is the center of the circle, AB is side of a regular pentagon, then angle ACB is equal to :

  1. 36°

  2. 72°

  3. 50°

  4. 40°

In the given figure, O is the center of the circle, AB is side of a regular pentagon, then angle ACB is equal to : Circles, Concise Mathematics Solutions ICSE Class 10.

Circles

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Answer

Join OA and OB.

In the given figure, O is the center of the circle, AB is side of a regular pentagon, then angle ACB is equal to : Circles, Concise Mathematics Solutions ICSE Class 10.

Given,

AB is side of a regular pentagon.

∴ ∠AOB = 360°5\dfrac{360°}{5} = 72°.

We know that,

The angle which an arc of a circle subtends at the center is double that which it subtends at any point on the remaining part of the circumference.

∴ ∠AOB = 2∠ACB

∠ACB = AOB2=72°2\dfrac{∠AOB}{2} = \dfrac{72°}{2} = 36°.

Hence, Option 1 is the correct option.

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