is a tangent to a circle at point . is a triangle inscribed in the circle. If angle and angle , calculate the size of angle .

Answer and explanation

Correct answer: A.

  1. Step 1: Apply the Alternate Segment Theorem: the angle between tangent and chord equals the angle subtended by chord in the alternate segment: .
  2. Step 2: Use the triangle angle sum theorem in : the interior angles of a triangle sum to : .
  3. Step 3: Substitute the known angles: .
Answer
.
Why not the others: is angle ; is angle ; subtracts incorrectly ().

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