document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=513387>Question 513387</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Verify, <BR>\n" );
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document.write( "cosxcosy = 1/2 [cos(x+y) + cos(x-y)]<BR>\n" );
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document.write( "My professor did not properly explain this. I don't understand how to solve the equation.<BR>\n" );
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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 #343554 by </B><A HREF=/tutors/aboutme.mpl?userid=lwsshak3><B>lwsshak3(11628)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=lwsshak3><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=343554\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> verify:<BR>\n" );
document.write( "cosxcosy = 1/2 [cos(x+y) + cos(x-y)]<BR>\n" );
document.write( "starting from right side:<BR>\n" );
document.write( "using addition formulas<BR>\n" );
document.write( "1/2[(cosxcosy-sinxsiny)+((cosxcosy+sinxsiny)]<BR>\n" );
document.write( "=1/2(2cosxcosy)=cosxcosy<BR>\n" );
document.write( "verified:<BR>\n" );
document.write( "right side = left side </SPAN>\n" );
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