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<p>could someone please explain how to do this? i forget the answer sorry!</p>
<p>Since a square is inscribed in the circle, you know that it has been divided into 4 equal parts. To get arc ST you simply divide 360 by 4 and you get 90 degrees.</p>
<p>Sent from my DROID2 using CC</p>
<p>Exactly. You know a circle has 360 degrees, and the square has divided the circle into 4 equal arcs. Therefore, one arc has a measure of 360/4=90</p>
<p>You could just remember the circle theories that say that an inscribed angle=the corresponding arc; therefore it follows that an inscribed angle of 90 degrees equals a corresponding arc.</p>
<p>central angle ( from center ) = 2 Inscribed angle = 2 measure of the arc
you got inscribed angle = 90 then measure of the arc = 180 (arc RST)
Question asks for half of it then it’s 90.</p>