document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=925555>Question 925555</A>: <I><SPAN STYLE=\"word-break: break-all;\"> How do I evaluate these this two sine and cosine problems. Difficult!?<BR>\n" );
document.write( "Evaluate cos(a &#8722; b) if cos a = 4/5 tan a < 0, tan b = &#8722;&#8730;15 and cos b < 0 <BR>\n" );
document.write( "cos(a-b) = \r<BR>\n" );
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document.write( "and \r<BR>\n" );
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document.write( "Evaluate sin(x + y) if sin x = 3/5 sec x > 0, cos y = &#8722; (2&#8730;5)/5 and tan y < 0. <BR>\n" );
document.write( "sin(x + y) = \r<BR>\n" );
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document.write( "THANKS! <BR>\n" );
document.write( " </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #561656 by </B><A HREF=/tutors/aboutme.mpl?userid=stanbon><B>stanbon(75887)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=stanbon><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=561656\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> evaluate these this two sine and cosine problems. Difficult!?<BR>\n" );
document.write( " Evaluate:: <BR>\n" );
document.write( "cos(a &#8722; b) if cos a = 4/5 tan a < 0,<BR>\n" );
document.write( "Note:: a is in QII where x is positive and y is negative<BR>\n" );
document.write( "Since cos = x/r, x = 4 and y = -sqrt(5^2-4^2) = -3<BR>\n" );
document.write( "Then sin(a) = y/r = -3/4<BR>\n" );
document.write( "------------------ <BR>\n" );
document.write( "tan b = &#8722;&#8730;15 and cos b < 0<BR>\n" );
document.write( "Note:: b is in QII where x is negative and y is positive<BR>\n" );
document.write( "Since tan = y/x, y = sqrt(15) and x = -1<BR>\n" );
document.write( "Then sin(b) = y/r = sqrt(15)/sqrt((sqrt(15))^2+1^2) = sqrt(15)/4<BR>\n" );
document.write( "and cos(b) = x/r = -1/4<BR>\n" );
document.write( "--------------------------------------------- <BR>\n" );
document.write( "cos(a-b) = cos(a)cos(b)+sin(a)sin(b)<BR>\n" );
document.write( "----<BR>\n" );
document.write( "= (4/5)*(-1/4) + (-3/4)(sqrt(15)/4)<BR>\n" );
document.write( "===================================== \r<BR>\n" );
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document.write( "\n" );
document.write( "  <BR>\n" );
document.write( "and <BR>\n" );
document.write( "Evaluate sin(x + y) if sin x = 3/5 sec x > 0, cos y = &#8722; (2&#8730;5)/5 and tan y < 0. <BR>\n" );
document.write( "sin(x + y) =<BR>\n" );
document.write( "---Whoops:: Got to run.  Maybe you can finish this now.<BR>\n" );
document.write( "Cheers,<BR>\n" );
document.write( "Stan H.<BR>\n" );
document.write( "------------ <BR>\n" );
document.write( " </SPAN>\n" );
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