document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=809977>Question 809977</A>: <I><SPAN STYLE=\"word-break: break-all;\"> I want to know the prove on double angle identities,<BR>\n" );
document.write( "  Please explain with detail step by step and give examples. please help me, i need it thank you. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #487912 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=487912\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\">  I want to know the prove on double angle identities,<BR>\n" );
document.write( "------<BR>\n" );
document.write( "Since sin(a+b) = sin(a)cos(b)+cos(a)sin(b),<BR>\n" );
document.write( "sin(2x) = sin(x+x) = sin(x)cos(x)+cos(x)sin(x) = 2sin(x)cos(x)<BR>\n" );
document.write( "-----<BR>\n" );
document.write( "Since cos(a-b) = cos(a)cos(b)-sin(a)sin(b)<BR>\n" );
document.write( "cos(2x) = cos(x+x) = cos(x)cos(x)- sin(x)sin(x) = cossin^2(x)-cos^2(x)<BR>\n" );
document.write( "-----<BR>\n" );
document.write( "tan(2x) = sin(2x)/cos(2x)<BR>\n" );
document.write( "-----<BR>\n" );
document.write( "= [2sin(x)cos(x)]/[cos^2(x)-sin^2(x)]<BR>\n" );
document.write( "Divide numerator and denominator by cos^2(x) to get:<BR>\n" );
document.write( "= 2tan(x)/(1-tan^2(x))<BR>\n" );
document.write( "==============<BR>\n" );
document.write( "Cheers,<BR>\n" );
document.write( "Stan H.<BR>\n" );
document.write( "============== </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );