document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1077273>Question 1077273</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Hi can someone help me with this problem please? THANK YOU! \r<BR>\n" );
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document.write( "   Find the exact value of cos(2 theta)\r<BR>\n" );
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document.write( "          cos(theta)=-15/17 and theta terminates in QII.\r<BR>\n" );
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document.write( "         a.-240/289<BR>\n" );
document.write( "         b.161/289<BR>\n" );
document.write( "         c.120/289<BR>\n" );
document.write( "         d.16/17 </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #691817 by </B><A HREF=/tutors/aboutme.mpl?userid=htmentor><B>htmentor(1343)</B></A><img src=\"/images/stars/stars-12.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=htmentor><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/cgi-bin/show-face.mpl?user=htmentor><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=691817\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Given that cos(t) = -15/17, we know the adjacent side is 15 (QII) and the hypotenuse is 17.<BR>\n" );
document.write( "Let the opposite side by x.  Then sin(t) = x/17<BR>\n" );
document.write( "From the Pythagorean theorem we know that x^2 = 17^2 - 15^2<BR>\n" );
document.write( "We can make use of the identity, cos(2t) = cos^2(t) - sin^2(t)<BR>\n" );
document.write( "sin^2(t) = x^2/17^2 = (17^2-15^2)/17^2 = 1 - (15/17)^2<BR>\n" );
document.write( "Therefore, cos(2t) = (-15/17)^2 - [1-(15/17)^2] = (450-289)/289  = 161/289<BR>\n" );
document.write( "Ans: b </SPAN>\n" );
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