document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=810786>Question 810786</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Find cos(2 theta)<BR>\n" );
document.write( "Given : tan theta = 12/5, theta is in quadrant 3 </SPAN>\n" );
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document.write( "Given : tan theta = 12/5, theta is in quadrant 3<BR>\n" );
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document.write( "Note: Both x and y are negative in QIII<BR>\n" );
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document.write( "Since tan = y/x = 12/5, y = -12 and x = -5<BR>\n" );
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document.write( "Then r = sqrt[12^2+5^2] = sqrt[169] = 13<BR>\n" );
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document.write( "cos = x/r = -5/13<BR>\n" );
document.write( "sin = y/4 = -12/13<BR>\n" );
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document.write( "Your Problem::<BR>\n" );
document.write( "cos(2 t) = cos^2(t)-sin^2(t) = (5/13)^2 - (12/13)^2 = (25-144)/169 = -119/169<BR>\n" );
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document.write( "Cheers,<BR>\n" );
document.write( "Stan H.<BR>\n" );
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