Q.In a circle with center O, PQ and PR are two chords. Tangents drawn at points Q and P intersect at point S. If ∠QSR = 70°, then what is the measure of ∠QPR?

Since OQ and OR are radii drawn to the points of tangency of the tangents, Therefore, ∠OQS and ∠ORS are both 90°. In quadrilateral OQSR: ∠QOR = 360° − (∠OQS + ∠ORS + ∠QSR) = 360° − (90° + 90° + 70°) = 360° − 250° = 110° Now, ∠QOR is the central angle subtending arc QTR, and ∠QPR is the inscribed angle subtending the same arc. Therefore, ∠QPR = ½ × ∠QOR = ½ × 110° = 55°
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