In triangle PQR, the perpendicular bisectors OX, OY, and OZ meet at O (the circumcenter).\nGiven ∠QPR = 65° and ∠PQR = 60°, find the value (in degrees) of ∠QOR + ∠POR.

Difficulty: Medium

Correct Answer: 250

Explanation:


Introduction / Context:
This problem uses the circumcenter O of triangle PQR. The perpendicular bisectors of the three sides meet at O. For any arc in a circle, the central angle at O is twice the inscribed angle that subtends the same chord. We will convert given vertex angles into corresponding central angles and then add them appropriately.


Given Data / Assumptions:

  • ∠QPR = 65° (angle at P)
  • ∠PQR = 60° (angle at Q)
  • O is the circumcenter; ∠QOR subtends arc QR; ∠POR subtends arc PR.


Concept / Approach:
In a circumcircle, a central angle equals twice the inscribed angle that subtends the same arc. Therefore, ∠QOR = 2 * ∠QPR and ∠POR = 2 * ∠PQR. Sum them to obtain the target value.


Step-by-Step Solution:

∠QOR = 2 * ∠QPR = 2 * 65° = 130°∠POR = 2 * ∠PQR = 2 * 60° = 120°∠QOR + ∠POR = 130° + 120° = 250°


Verification / Alternative check:
Using triangle angle sum, ∠PRQ = 180° − (65° + 60°) = 55°. The three corresponding central angles would be 130°, 120°, and 110°, which sum to 360°, consistent with a full circle. Our selected pair (130° and 120°) adds to 250° as computed.


Why Other Options Are Wrong:

  • 180: Would require ∠QPR + ∠PQR = 90°, which is not the case.
  • 210 or 125: Do not match 2*(65°) + 2*(60°).


Common Pitfalls:

  • Confusing the inscribed angle with the central angle (forgetting the factor 2).
  • Using the wrong vertex angle for a given arc.


Final Answer:
250

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