<PRE><B>Question 920260</B>
Find cos 2&amp;#952;. sin &amp;#952; = 24/25 , &amp;#952; lies in quadrant I in which sin&gt;0, cos&gt;0
sin^2&amp;#952;+cos^2&amp;#952;=1
cos^2&amp;#952;=1-sin^2&amp;#952;
cos&amp;#952;=&amp;#8730;(1-sin^2&amp;#952;)=&amp;#8730;(1-(24/25)^2)=&amp;#8730;(1-(576/625))=&amp;#8730;(49/625)=7/25
cos2&amp;#952;=cos^2&amp;#952;-sin^2&amp;#952;=49/625-576/625=-527/625
check:
sin&amp;#952;=24/25
&amp;#952;&amp;#8776;73.74&amp;#730;
2&amp;#952;&amp;#8776;147.48&amp;#730;
cos2&amp;#952;=cos(147.48&amp;#730;)&amp;#8776;-0.8432...
Exact value=-527/625&amp;#8776;-0.8432...</PRE>