document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1126039>Question 1126039</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Express as a product\r<BR>\n" );
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document.write( "cosa+2cos7a+cos13a\r<BR>\n" );
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document.write( "I know formulas but not how to apply </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #742469 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=742469\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Express as a product\r<BR>\n" );
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document.write( "cosa+2cos7a+cos13a = (1/4)*(4cosa + 8cos7a + 4cos13a) </SPAN>\n" );
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