document.write( "Question 1159220: Use the given conditions to find the exact value of the expression.
\n" ); document.write( "cos α = 24/25, sin α < 0,cos(a+ 11π/6)\r
\n" ); document.write( "\n" ); document.write( "I am not sure if i just substitute 24/25 for a in the cos(a+11pi/6)\r
\n" ); document.write( "\n" ); document.write( "I did that and got (144+275pi)/(150) which is incorrect. What am I doing wrong? Please help...\r
\n" ); document.write( "\n" ); document.write( " \n" ); document.write( "

Algebra.Com's Answer #782192 by ikleyn(52781) $\"\"$ $\"About$

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

\r\n" );
document.write( "\r\n" );
document.write( "Use the formula for sum of arguments\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "    cos(a+b) = cos(a)*cos(b) - sin(a)*sin(b)    (1)\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "You need to know sin(a) and sin(b) and cos(b)\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "sin(a) = +/-  = +/-  = +/-  = +/- ,\r\n" );
document.write( "\r\n" );
document.write( "and since  sin(a) < 0, according to the condition, we chose  sin(a) = -.    (2)\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "Next, b =  = ;\r\n" );
document.write( "\r\n" );
document.write( "therefore, sin(b) = -;  cos(b) = .    (3)\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "Now the last YOUR step is to substitute  (2) and (3) into the formula (1).\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "You do it and complete the calculations on your own.\r\n" );
document.write( "

\r
\n" ); document.write( "\n" ); document.write( "-------------\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "At this point I complete my explanations.\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "Do you understand them in full ?\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "You can report about your progress to me.\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "If you complete successfully and report to me, you will get a present/(a gift) from me.\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( " \n" ); document.write( "

\n" );