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In the given figure, AB is a diameter of a circle with centre O and chord ED is parallel to AB and ∠EAB = 65°. Calculate : (i) ∠EBA (ii) ∠BED (iii) ∠BCD

In the given figure, AB is a diameter of a circle with centre O and chord ED is parallel to AB and ∠EAB = 65°. Loci, RSA Mathematics Solutions ICSE Class 10.

Circles

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Answer

(i) We know that,

Angle in semi-circle is a right angle.

∴ ∠AEB = 90°.

In △AEB,

⇒ ∠AEB + ∠EBA + ∠EAB = 180°

⇒ 90° + ∠EBA + 65° = 180°

⇒ 155° + ∠EBA = 180°

⇒ ∠EBA = 180° - 155° = 25°.

Hence, ∠EBA = 25°.

(ii) ∠BED = ∠EBA = 25° Alternate interior angles ED ∥ AB, EB as a transversal

Hence, ∠BED = 25°.

(iii) As, AB ∥ ED

∴ ∠DEB = ∠EBA = 25° [Alternate angles]

BCDE is a cyclic quadrilateral.

∴ ∠DEB + ∠BCD = 180° [Sum of opposite angles in a cyclic quadrilateral = 180°.]

⇒ 25° + ∠BCD = 180°

⇒ ∠BCD = 180° - 25° = 155°.

Hence, ∠BCD = 155°.

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