document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1064867>Question 1064867</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Please help me find Cos(A-b) in the following equation.\r<BR>\n" );
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document.write( "Equation: https://s28.postimg.org/fbpu1fv25/tan_a_5.png<BR>\n" );
document.write( "Thanks.  </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #680116 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=680116\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> cos (a-b)=cos a*cos b-sin a*sin b<BR>\n" );
document.write( "A is a right triangle on the unit circle with adjacent -1, opposite -5, and hypotenuse sqrt (26). <BR>\n" );
document.write( "B is a right triangle with adjacent -sqrt(5), opposite +2, and hypotenuse 3.<BR>\n" );
document.write( "cos a=-1/sqrt (26)<BR>\n" );
document.write( "cos b=-sqrt (5)/3.  Their product is +sqrt (5)/3 sqrt (26), and rationalized that is sqrt (130)/78.<BR>\n" );
document.write( "sin a =-5/sqrt(26)<BR>\n" );
document.write( "sin b=2/3.  Their product is -10/3 sqrt (26) and rationalized, that is -10 sqrt (26)/78.  We are subtracting this second product from the first, so the answer is D, sqrt(130)+10 sqrt (26) divided all by 78. </SPAN>\n" );
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