document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1033303>Question 1033303</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Use the half-angle identity to find the exact value of cos([7pi]/[12]) </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #647891 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=647891\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\">  Use the half-angle identity to find the exact value of cos([7pi]/[12]) <BR>\n" );
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document.write( "cos[7pi/6] = ?<BR>\n" );
document.write( "Reference angle = pi/6<BR>\n" );
document.write( "7pi/6 is in QIII where cos is negative<BR>\n" );
document.write( "So, cos[7pi/6] = -cos(pi/6) = -sqrt(3)/2<BR>\n" );
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document.write( "Note::   7pi/12 = (1/2)[7pi/6]<BR>\n" );
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document.write( "Formula::  cos(x/2) = sqrt[(1+cos(x)/2])<BR>\n" );
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document.write( "Therefore:: cos[7pi/12] = cos[(7pi/6)/2] = sqrt[(1+cos(7pi/6)/2))<BR>\n" );
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document.write( "= sqrt[(1-sqrt(3))/2)/2] = sqrt[(1-sqrt(3))/4]<BR>\n" );
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document.write( "Cheers,<BR>\n" );
document.write( "Stan H.<BR>\n" );
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