document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1136950>Question 1136950</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A is an obtuse angle such that cos(A)=-4/5. Find:\r<BR>\n" );
document.write( "\n" );
document.write( "1. Cos(4A).\r<BR>\n" );
document.write( "\n" );
document.write( "2. Sin (4A). </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #754798 by </B><A HREF=/tutors/aboutme.mpl?userid=Alan3354><B>Alan3354(69443)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=Alan3354><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=Alan3354><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=754798\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> A is an obtuse angle such that cos(A)=-4/5. <BR>\n" );
document.write( "----<BR>\n" );
document.write( "The terminal point is in Q2.<BR>\n" );
document.write( "======\r<BR>\n" );
document.write( "\n" );
document.write( "Find:\r<BR>\n" );
document.write( "\n" );
document.write( "1. Cos(4A)<BR>\n" );
document.write( "cos(2A) = 2cos^2(A) - 1 = 32/25 - 1 = 7/25<BR>\n" );
document.write( "---<BR>\n" );
document.write( "cos(4A) = 2*(7/25)^2 - 1 = 98/625 - 1<BR>\n" );
document.write( "= -527/625<BR>\n" );
document.write( "=====================================<BR>\n" );
document.write( "2. Sin (4A)<BR>\n" );
document.write( "sin(4A) = sqrt(1 - cos^2(4A))<BR>\n" );
document.write( "= sqrt(390625/390625 - 277729/390625)<BR>\n" );
document.write( "= sqrt(112896/390625)<BR>\n" );
document.write( "= -336/625<BR>\n" );
document.write( " </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );