document.write( "Question 1053554: 10cos^2x+9cosx+2=0 find all solution in the interval [0,360)?
\n" ); document.write( "the answer is 113.58,246.42,120,240
\n" ); document.write( "i needed step by step solution \n" ); document.write( "

Algebra.Com's Answer #668774 by Fombitz(32388) $\"\"$ $\"About$

You can put this solution on YOUR website!
Use a substitution,
\n" ); document.write( " $\"u=cos%28theta%29\"$
\n" ); document.write( " $\"10u%5E2%2B9u%2B2=0\"$
\n" ); document.write( "Now just solve it like a quadratic equation,
\n" ); document.write( "Factoring,
\n" ); document.write( " $\"%285u%2B2%29%282u%2B1%29=0\"$
\n" ); document.write( "So then,
\n" ); document.write( " $\"5u%2B2=0\"$
\n" ); document.write( " $\"5u=-2\"$
\n" ); document.write( " $\"u=-2%2F5\"$
\n" ); document.write( " $\"cos%28theta%29=-2%2F5\"$
\n" ); document.write( "Use a calculator to solve for the two values.
\n" ); document.write( "and,
\n" ); document.write( " $\"2u%2B1=0\"$
\n" ); document.write( " $\"2u=-1\"$
\n" ); document.write( " $\"u=-1%2F2\"$
\n" ); document.write( " $\"cos%28theta%29=-1%2F2\"$
\n" ); document.write( "Again use a calculator or from your previous studies,
\n" ); document.write( " $\"theta=120\"$ and $\"theta=240\"$
\n" ); document.write( " \n" ); document.write( "

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