document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=467906>Question 467906</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Find the exact value of sin 2a, cos 2a, and tan2 a given that:\r<BR>\n" );
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document.write( "cos a=-2/11 and a is  in Quadrant III\r<BR>\n" );
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document.write( "I need help understanding exactly how to derive the conclusions please.  I am soo lost. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #321072 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=321072\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Find the exact value of sin 2a, cos 2a, and tan2 a given that: <BR>\n" );
document.write( "cos a=-2/11 and a is in Quadrant III <BR>\n" );
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document.write( "sin(2a) = 2sin(a)cos(a)<BR>\n" );
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document.write( "Find sin(a):<BR>\n" );
document.write( "Since cos(a) = x/r = -2/11 in QII<BR>\n" );
document.write( "x = -2 and r = 11<BR>\n" );
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document.write( "Then y = sqrt[11^2-2^2] = sqrt(117]<BR>\n" );
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document.write( "So sin(a) = y/r = sqrt(117)/11<BR>\n" );
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document.write( "Then sin(2a) = 2(sqrt(117)/11*(-2/11) = -4sqrt(11)/121<BR>\n" );
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document.write( "Using sin(a) and cos(a) you can find cos(2a) = cos^2-sin^2<BR>\n" );
document.write( "and tan(2a) = sin(2a)/cos(2a)<BR>\n" );
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document.write( "Keep in mind that your \"a\" is in the 2nd Quadrant.<BR>\n" );
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document.write( "Cheers,<BR>\n" );
document.write( "Stan H.    </SPAN>\n" );
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