document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=927015>Question 927015</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Suppose sin(X) = 4/5, and the terminal side of X is in quadrant II.<BR>\n" );
document.write( "A.Find cos(x). <BR>\n" );
document.write( "B.Use a double-angle formula to find sin(2x). <BR>\n" );
document.write( "C.Use a double-angle formula to find cos(2x) </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #562659 by </B><A HREF=/tutors/aboutme.mpl?userid=lwsshak3><B>lwsshak3(11628)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=lwsshak3><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=562659\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Suppose sin(X) = 4/5, and the terminal side of X is in quadrant II.<BR>\n" );
document.write( "A.Find cos(x)=-3/5 (working with a (3-4-5) reference right triangle in quadrant II where sin>0, cos<0<BR>\n" );
document.write( "B.Use a double-angle formula to find sin(2x)=2sinxcosx=2*4/5*-3/5=-24/25<BR>\n" );
document.write( "C.Use a double-angle formula to find cos(2x)=cos^2(x)-sin^2(x)=9/25-16/25=-7/25<BR>\n" );
document.write( "check:<BR>\n" );
document.write( "sinx=4/5<BR>\n" );
document.write( "x&#8776;126.87&#730;<BR>\n" );
document.write( "2x=253.74<BR>\n" );
document.write( "sin(2x)=sin(253.74)&#8776;-0.9600<BR>\n" );
document.write( "exact value as computed=-24/25=-0.9600<BR>\n" );
document.write( "cos(2x)=cos(253.74)&#8776;-0.2800 <BR>\n" );
document.write( "exact value as computed=-7/25=-0.2800 </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );