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In the adjoining figure, PQ and PR are tangents from P to a circle with centre O. If ∠POR = 55°, then ∠QPR is

  1. 35°

  2. 55°

  3. 70°

  4. 80°

In the adjoining figure, PQ and PR are tangents from P to a circle with centre O. If ∠POR = 55°, then ∠QPR is (a) 35° (b) 55° (c) 70° (d) 80°. Circles, ML Aggarwal Understanding Mathematics Solutions ICSE Class 10.

Circles

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Answer

OR ⊥ PR (∵ radius of a circle and tangent through that point are perpendicular to each other.)

∴ ∠ORP = 90°.

Since, sum of angles in a triangle = 180°.

⇒ ∠ORP + ∠POR + ∠OPR = 180°
⇒ 90° + 55° + ∠OPR = 180°
⇒ 145° + ∠OPR = 180°
⇒ ∠OPR = 180° - 145°
⇒ ∠OPR = 35°.

∠QPO = ∠OPR = 35° (∵ the tangents are equally inclined to the line joining the point and the centre of the circle.)

From figure,

∠QPR = ∠OPR + ∠QPO = 35° + 35° = 70°.

Hence, Option 3 is the correct option.

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