Since the line segment PQ is tantgent to the circle, then the angle mTherefore we know that the angle OQR has to be 30°. This is shown in the figure:
Now, we know that the sum of all the internal angles of a triangle must be 180°, then for the triangle RQP we have:

For the triangle OQR we have

and for the triangle OQP we have

Summing up we have the system

At first glance we see that this system hava more unknown variables than equations, but we have to notice that the angles alpha and gamma are supplementary, then
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