document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=924665>Question 924665</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Use an Addition or Subtraction Formula to write the expression as a trigonometric function of one number.<BR>\n" );
document.write( "cos(4pi/7)cos(5pi/21)+ sin(4pi/7)sin(5pi/21)  =\r<BR>\n" );
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document.write( "Find its exact value.<BR>\n" );
document.write( "cos(4pi/7)cos(5pi/21)+ sin(4pi/7)sin(5pi/21)  =\r<BR>\n" );
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document.write( "Please explain<BR>\n" );
document.write( "Thank you </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #561013 by </B><A HREF=/tutors/aboutme.mpl?userid=Alan3354><B>Alan3354(69443)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=Alan3354><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=Alan3354><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=561013\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Use an Addition or Subtraction Formula to write the expression as a trigonometric function of one number.<BR>\n" );
document.write( "cos(4pi/7)cos(5pi/21)+ sin(4pi/7)sin(5pi/21)  =<BR>\n" );
document.write( "-----------<BR>\n" );
document.write( "Look up the formula for cos(A-B)<BR>\n" );
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