Question : In the given figure, O is the centre of the circle. The circle has 3 tangents. If $\angle QPR=45^{\circ}$, then what is the value (in degrees) of $\angle QOR$?
Option 1: 67.5
Option 2: 72
Option 3: 78.5
Option 4: 65
Correct Answer: 67.5
Solution :
Given that the tangents from an external point to a circle are equal in length.
Such that $QS = QT$ and $RU = RT$.
Assume that the $\angle SQO$, $\angle OQT$, $\angle TRO$, and $\angle ORU$ as $x$.
Such that $\angle PQR=\angle PRQ=180^{\circ} - 2x$.
In $\triangle PQR$,
$\angle PQR+\angle PRQ+\angle QPR=180^{\circ}$
⇒ $(180^{\circ} - 2x)+(180^{\circ} - 2x)+45^{\circ}=180^{\circ}$
⇒ $x=56.25^{\circ}$
In $\triangle OQR$,
⇒ $x+x+\angle OQR=180^{\circ}$
⇒ $2x+\angle OQR=180^{\circ}$
⇒ $2(56.25^{\circ}) +\angle OQR=180^{\circ}$
⇒ $\angle QOR=67.5^{\circ}$
Hence, the correct answer is 67.5.
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