In a ∆PQR, S is any point on side QR. Internal bisector of ∠PQS and ∠PSQ meet at I1, Internal bisector of ∠PSR, and ∠PRS meet at I2. If ∠QI1S = 100°, ∠SI2R = 120°, O is orthocentre of ∆PQR, then what is the measure of ∠QOR?
In a ∆PQR, S is any point on side QR. Internal bisector of ∠PQS and ∠PSQ meet at I1, Internal bisector of ∠PSR, and ∠PRS meet at I2. If ∠QI1S = 100°, ∠SI2R = 120°, O is orthocentre of ∆PQR, then what is the measure of ∠QOR? Correct Answer 100°
Given:
∠QI1S = 100°, ∠SI2R = 120°
Calculation:
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∠QI1S = 90° + (∠QPS/2)
⇒ 100° = 90° + (∠QPS/2)
⇒ ∠QPS/2 = 10°
⇒ ∠QPS = 20°
∠SI2R = 90° + (∠SPR/2)
⇒ 120° = 90° + (∠SPR/2)
⇒ ∠SPR/2 = 30°
⇒ ∠SPR = 60°
∠P = ∠QPS + ∠SPR
⇒ ∠P = 20° + 60° = 80°
∠QOR = 180° – ∠P
⇒ ∠QOR = 180° – 80°
∴ ∠QOR = 100°
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Feb 20, 2025