document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1089214>Question 1089214</A>: <I><SPAN STYLE=\"word-break: break-all;\"> verify the identity. \r<BR>\n" );
document.write( "\n" );
document.write( "cos (x + pi/2) = - sin x </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #703551 by </B><A HREF=/tutors/aboutme.mpl?userid=Theo><B>Theo(13342)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=Theo><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=Theo><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=703551\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> this uses the basic trigonometric identity of:\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "cos(a + b) = cos(a) * cos(b) - sin(a) * sin(b).\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "replace a with x and b with pi/2 and you get:\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "cos(x + pi/2) = cos(x) * cos(pi/2) - sin(x) * sin(pi/2)\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "cos(pi/2) = 0\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "sin(pi/2) = 1\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "you can use your calculator to confirm.\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "equation bec0omes:\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "cos(x + pi/2) = cos(x) * 0 - sin(x) * 1\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "simplify to get:\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "cos(x + pi/2) = -sin(x)\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "QED (that's your solution).\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "<BR>\n" );
document.write( "<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( " </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );