document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=194974>Question 194974</A>: <I><SPAN STYLE=\"word-break: break-all;\"> How do you verify cos(A+B)+cos(A-B)=2cosAcosB </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #146251 by </B><A HREF=/tutors/aboutme.mpl?userid=jim_thompson5910><B>jim_thompson5910(35256)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=jim_thompson5910><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=146251\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> I'd start with the left side and work my way to get it equal to the right side (if you go with the left side, do NOT change the right).\r<BR>\n" );
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document.write( "Recall the identities:\r<BR>\n" );
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document.write( "cos(A+B) = cos(A)cos(B)-sin(A)sin(B), and\r<BR>\n" );
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document.write( "cos(A-B) = cos(A)cos(B)+sin(A)sin(B)\r<BR>\n" );
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document.write( "cos(A+B)+cos(A-B)=2cos(A)cos(B) ... Start with the given equation.\r<BR>\n" );
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document.write( "[cos(A)cos(B)-sin(A)sin(B)]+cos(A-B)=2cos(A)cos(B) ... Use the first identity given above\r<BR>\n" );
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document.write( "[cos(A)cos(B)-sin(A)sin(B)]+[cos(A)cos(B)+sin(A)sin(B)]=2cos(A)cos(B) ... Use the second identity given above\r<BR>\n" );
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document.write( "[cos(A)cos(B)+cos(A)cos(B)]+[-sin(A)sin(B)+sin(A)sin(B)]=2cos(A)cos(B) ... Rearrange the terms.\r<BR>\n" );
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document.write( "2cos(A)cos(B)+0=2cos(A)cos(B) ... Combine like terms.\r<BR>\n" );
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document.write( "2cos(A)cos(B)=2cos(A)cos(B) ... Simplify\r<BR>\n" );
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document.write( "Since both sides are equal, we've verified the identity. </SPAN>\n" );
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