<p><a href="http://imageshack.us/a/img841/2658/ton6.png%5B/url%5D">http://imageshack.us/a/img841/2658/ton6.png</a></p>
<p>Angle PRQ is a right angle because RQ is a tangent line. PR is 6, and PQ is 6 + 1 = 7. By the Pythagorean theorem, RQ is squareroot of 13. SQ is 1, so RS is (squareroot of 13) - 1.</p>
<p>Sorry for no symbols. Where does the problem come from? It is not a particularly hard one.</p>