document.write( "Question 1183332: Find an identity for cos(4t) in terms of cos(t).\r
\n" ); document.write( "\n" ); document.write( "cos(4t) = \n" ); document.write( "

Algebra.Com's Answer #813606 by ikleyn(53925) $\"\"$ $\"About$

You can put this solution on YOUR website!
.
\n" ); document.write( "

\r\n" );
document.write( "\r\n" );
document.write( "Use the general trigonometric formula\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "    cos(2a) = 2cos^2(a) - 1.\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "twice.  It gives \r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "    cos(4t) = 2cos^2(2t) - 1 = 2*(2cos^2(t)-1)^2 - 1 = 2*(4cos^4(t) - 4cos^2(t) +1) - 1 = \r\n" );
document.write( "\r\n" );
document.write( "            = 8cos^4(t) - 8cos^2(t) + 1.     ANSWER\r\n" );
document.write( "

\r
\n" ); document.write( "\n" ); document.write( "Solved and carefully explained.\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( " \n" ); document.write( "

\n" );