<p><a href="http://tinypic.com/view.php?pic=65y7ia&s=8">http://tinypic.com/view.php?pic=65y7ia&s=8</a></p>
<p>You may be able to use s=r theta</p>
<p>PR is 5, the radius is also 5, draw OR (another radii) and you’ve got an equilateral. Since the arc is proportional to the central angle, you’ve got 60/360 or 1/6</p>
<p>wow thanks a lot . i just got it</p>
<p>Answer: 1/6
How do I know? It’s pretty easy actually.
PC is the diameter of the circle and it’s equal to 10. This means that the radius PO=OS=5. There is one more radius in the picture and I’m talking about RO (the “invisible” one). Then you notice that you’ve got a triangle PRO with sides PR=RO=PO=5. It’s an equilateral triangle which means that it has 3 equal angles in it. We know that the sum of the angles in every triangle is 180 degrees, so when we divide 180 by 3 we get that angle ORP = angle POR = angle RPO = 60 degrees. But we also notice that POR is a central angle. The arc PQR equals to 60 too, because the radii PO and RO which form the central angle stand on the edges of the arc. Thus, we make a fraction or ratio which looks like this: arc PQR / 360 degrees = 60 / 360 = 1/6
And that’s it! If you want you can try the following formula in order to find the length of the arc and then to divide it by the circumference of the circle. Central angle / 360 degrees = Arc length / 2Пr (where П=3.14 and r=5). Maybe some of the numbers you’ll get will need some rounding, but you’ll get the same answer.</p>