# Chapter 6 - Section 6.1 - Circles and Related Segments and Angles - Exercises - Page 285: 10d

60$^{\circ}$

#### Work Step by Step

$\angle$STR=90 because it is inscribed in a semicircle. Since ST is equal to half SR (the hypotenuse of STR), then STR is a 30 60 90 triangle. Angle S is across from the longer leg of the triangle so its measure is 60$^{\circ}$.

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