Question 878451
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Since any tangent to a point on a circle is orthogonal to the radius at that point, angle OST, an therefore angle RST is right.  Since the Inscribed Angle Theorem says that an inscribed angle is one half the measure of the same arc subtended by the central angle.  A special case of this theorem (Thales Theorem) says that an angle subtended by a diameter is always right. Hence RAS is right.  Since RAS is right and RAT is straight, then SAT must be right. 


See if you can get where you need to go from that.


John
*[tex \LARGE e^{i\pi}\ +\ 1\ =\ 0]
My calculator said it, I believe it, that settles it
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