In the diagram, points R and S lie on QT. Also,∠PTQ=62∘, ∠RPS=34∘, and ∠QPR=x∘. What is the value of x?
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Solution
Since △PRS is isosceles with PR=PS, then ∠PRS=∠PSR. Since the angles in △PRS add to 180∘, then ∠PRS+∠PSR+∠RPS=180∘. Therefore, 2(∠PRS)+34∘=180∘ or 2(∠PRS)=146∘ or ∠PRS=73∘. Since △PQT is isosceles with PQ=PT, then ∠PQT=∠PTQ=62∘. Since ∠PRS is an exterior angle to △PQR, then ∠PRS=∠PQR+∠QPR or 73∘=62∘+x∘. Therefore, x=73−62=11. (Instead, we could have determined that ∠PRQ=180∘−∠PRS=180∘−73∘=107∘, and then looked at the sum of the angles in △PQR to get 62∘+x∘+107∘=180∘ or x=180−169=11.)
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