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For a triangle ABC with ∠B = 2∠C, the bisector of ∠A meets BC at D and ∠ADC = 100°. Find ∠C.

Competition practiceGeometry
  • A20°
  • B40°
  • C30°
  • D25°

Step-by-Step Solution

Let ∠, so ∠ and ∠. ∠ is an exterior angle of triangle . Setting this to 100 gives °.
Answer: A) 20°

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