document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=924818>Question 924818</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Could anyone please prove this: sin(x+y)sin(x-y)=cos^2(y)-cos^2(x) *involves adding and subtracting formulas. Pick only one side to do.  </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #561135 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=561135\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> sin(x+y)sin(x-y)=cos^2(y)-cos^2(x) <BR>\n" );
document.write( "------------------<BR>\n" );
document.write( "Using the left side::<BR>\n" );
document.write( "[sin(x)cos(y)+cos(x)sin(y)][sin(x)cos(y)-cos(x)sin(y)]<BR>\n" );
document.write( "----<BR>\n" );
document.write( "= [sin^2(x)cos^2y) - cos^2(x)sin^2(y)]<BR>\n" );
document.write( "----<BR>\n" );
document.write( "= [(1-cos^2(x))cos^2(y) - cos^2(x)(1-cos^2(y)]<BR>\n" );
document.write( "-----<BR>\n" );
document.write( "= [cos^2(y) - cos^2(x)cos^2(y) - cos^2(x) + cos^2(x)cos^2(y)]<BR>\n" );
document.write( "-----<BR>\n" );
document.write( "= cos^2(y) - cos^2(x)<BR>\n" );
document.write( "=========================<BR>\n" );
document.write( "Cheers,<BR>\n" );
document.write( "Stan H. </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );