document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=69282>Question 69282</A>: <I><SPAN STYLE=\"word-break: break-all;\"> If theta is an acute angle with cos theta=2/sqr rt 5, find the exact value of cos2 theta.\r<BR>\n" );
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document.write( "My possible answers are:<BR>\n" );
document.write( "-3/5<BR>\n" );
document.write( "-2/5<BR>\n" );
document.write( "2/5<BR>\n" );
document.write( "3/5 </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #49313 by </B><A HREF=/tutors/aboutme.mpl?userid=stanbon><B>stanbon(75887)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=stanbon><IMG SRC=http://www.algebra.com/images/aboutme-small.gif BORDER=0 alt=\"About Me\" VALIGN=MIDDLE></A>&nbsp;<IMG SRC=http://www.algebra.com/images/nopicture.jpg><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=49313\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> If theta is an acute angle with cos theta=2/sqr rt 5, find the exact value of cos2 theta. <BR>\n" );
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document.write( "cos(2x)=cos^2x-sin^2x<BR>\n" );
document.write( "You are given cosx=2/sqrt5<BR>\n" );
document.write( "Draw a right triangle with hyp=sqrt5 and side adjacent to angle x being 2<BR>\n" );
document.write( "Solve for the 3rd side which is sqrt((sqrt5)^2-2^2) = 1<BR>\n" );
document.write( "Then you have sin(x) = 1/sqrt5.<BR>\n" );
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document.write( "So cos(2theta) = cos^2(theta) - sin^2(theta)<BR>\n" );
document.write( "=(2/sqrt5)^2 - (1/sqrt5)^2<BR>\n" );
document.write( "=4/5 - 1/5<BR>\n" );
document.write( "= 3/5<BR>\n" );
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document.write( "Cheers,<BR>\n" );
document.write( "Stan H.\r<BR>\n" );
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