document.write( "Question 389103: Find, to the nearest degree, all values of x in the interval 0° ≤ x ≤ 360° that satisfy the equation 3 cos 2x + cos x + 2 = 0.\r
\n" ); document.write( "\n" ); document.write( "I need your help please! I tried, but unable to come up with an answer.\r
\n" ); document.write( "\n" ); document.write( "Thanks \n" ); document.write( "

Algebra.Com's Answer #275604 by Fombitz(32388) $\"\"$ $\"About$

You can put this solution on YOUR website!
Use the trig identity,
\n" ); document.write( " $\"cos%282x%29=2%28cos%28x%29%29%5E2-1\"$
\n" ); document.write( "So then,
\n" ); document.write( " $\"3%2Acos%282x%29=6%28cos%28x%29%29%5E2-3\"$
\n" ); document.write( "and then,
\n" ); document.write( " $\"3%2Acos%282x%29+%2B+cos%28x%29+%2B+2+=+0\"$
\n" ); document.write( " $\"6%28cos%28x%29%29%5E2-3%2Bcos%28x%29%2B2=0\"$ \r
\n" ); document.write( "\n" ); document.write( " $\"6%2A%28cos%28x%29%29%5E2%2Bcos%28x%29-1=0\"$
\n" ); document.write( "Use a substitution,
\n" ); document.write( "Let $\"u=cos%28x%29\"$
\n" ); document.write( " $\"6u%5E2%2Bu-1=0\"$
\n" ); document.write( "You can factor this quadratic or solve it using the quadratic formula.
\n" ); document.write( "Once you have the solution for $\"u\"$ , back substitute and find $\"x\"$ .
\n" ); document.write( " \n" ); document.write( "

\n" );