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Mathematics

ABCD is a cyclic quadrilateral such that AB is a diameter of the circle circumscribing it and ∠ADC = 125°, then ∠BAC is equal to :

  1. 35°

  2. 40°

  3. 45°

  4. 55°

Circles

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Answer

ABCD is a cyclic quadrilateral such that AB is a diameter of the circle circumscribing it and ∠ADC = 125°, then ∠BAC is equal to. Loci, RSA Mathematics Solutions ICSE Class 10.

Opposite angles of a cyclic quadrilateral are supplementary.

So,

∠ABC + ∠ADC = 180°

∠ABC = 180° − 125° = 55°.

∠ACB = 90° [Angle in semicircle is a right angle]

In △ABC,

By angle sum property of triangle,

∠BAC + ∠ABC + ∠ACB = 180°

∠BAC + 55° + 90° = 180°

∠BAC = 180° − 145° = 35°.

Hence, option 1 is the correct option.

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