document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1101605>Question 1101605</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Use product-to-sum identity to rewrite the expression\r<BR>\n" );
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document.write( "cos 40° cos 20°\r<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 #716200 by </B><A HREF=/tutors/aboutme.mpl?userid=Boreal><B>Boreal(15235)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=Boreal><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=Boreal><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=716200\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> cos(x)cos(y)=(1/2)&#8203;&#8203; [cos(x&#8722;y)+cos(x+y)]<BR>\n" );
document.write( "cos 40*cos 20=(1/2)[(cos 20)+cos (60)]<BR>\n" );
document.write( "Check<BR>\n" );
document.write( "cos 40*cos 20=0.7198<BR>\n" );
document.write( "cos 20+cos 60=1.44<BR>\n" );
document.write( "half of that is 0.72 (0.7198 with less rounding). </SPAN>\n" );
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