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In the given figure, ABCD is a cyclic quadrilateral whose side CD has been produced to E. If BA = BC and ∠BAC = 40°, find ∠ADE.

In the given figure, ABCD is a cyclic quadrilateral whose side CD has been produced to E. If BA = BC and ∠BAC = 40°, find ∠ADE. Loci, RSA Mathematics Solutions ICSE Class 10.

Circles

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Answer

Given,

Quadrilateral ABCD is a cyclic quadrilateral.

∠ACB = ∠CAB = 40° [Angles opposite to equal sides are equal]

By angle sum property of a triangle we get,

In ΔABC,

⇒ ∠CAB + ∠CBA + ∠ACB = 180°

⇒ 40° + ∠CBA + 40° = 180°

⇒ ∠CBA + 80° = 180°

∴ ∠CBA = 100°

∠CBA + ∠CDA = 180° [Sum of opposite angles in a cyclic quadrilateral = 180°]

⇒ 100° + ∠CDA = 180°

⇒ ∠CDA = 80°

∴ ∠CDA + ∠ADE = 180° [Linear pairs]

⇒ 80° + ∠ADE = 180°

⇒ ∠ADE = 100°.

Hence, the value of ∠ADE is 100°.

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