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O is the center of the circle and ∠AOC = 120°.

O is the center of the circle and ∠AOC = 120°. Concise Mathematics Solutions ICSE Class 10.

Statement (1) : ∠ABC = 120°

Statement (2) : ∠ABC + ∠ADC = 180° ⇒ ∠ABC + 60° = 180°.

O is the center of the circle and ∠AOC = 120°. Concise Mathematics Solutions ICSE Class 10.
  1. Both statements are true.

  2. Both statements are false.

  3. Statement 1 is true, and statement 2 is false.

  4. Statement 1 is false, and statement 2 is true.

Circles

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Answer

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

⇒ ∠AOC = 2 x ∠ADC

⇒ 120° = 2 x ∠ADC

⇒ ∠ADC = 120°2\dfrac{120°}{2} = 60°

ABCD form a cyclic quadrilateral and sum of opposite angles of cyclic quadrilateral is 180°.

⇒ ∠ADC + ∠ABC = 180°

⇒ 60° + ∠ABC = 180°

⇒ ∠ABC = 180° - 60°

⇒ ∠ABC = 120°

So, both statement are true.

Hence, option 1 is the correct option.

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