Arc is and arc is . What is the measure of ?
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Let the center of the circle be O . Given that arc B C and arc D A are 3 0 ∘ and 8 0 ∘ respectively, this means that the central angles, ∠ B O C = 3 0 ∘ and ∠ D O A = 8 0 ∘ . Since the angle at the circumference is half that of the central angle extended by the same arc, ∠ B A C = 1 5 ∘ and ∠ D C A = 4 0 ∘ . And since ∠ P + ∠ B A C = ∠ D C A , ⟹ ∠ P = ∠ D C A − ∠ B A C = 4 0 ∘ − 1 5 ∘ = 2 5 ∘ .