document.write( "Question 615390: Simplify this
\n" ); document.write( "(cos theta +1)(cos theta -1)
\n" ); document.write( " I cannot figer this out help me \n" ); document.write( "

Algebra.Com's Answer #387127 by jsmallt9(3758) $\"\"$ $\"About$

You can put this solution on YOUR website!
$\"%28cos%28theta%29%2B1%29%28cos%28theta%29+-1%29\"$
\n" ); document.write( "Just use FOIL or the $\"%28a%2Bb%29%28a-b%29+=+a%5E2-b%5E2\"$ pattern to multiply. I like using the patterns myself:
\n" ); document.write( " $\"cos%28theta%29%5E2-1%5E2%29\"$
\n" ); document.write( "which simplifies to:
\n" ); document.write( " $\"cos%28theta%29%5E2-1%29\"$
\n" ); document.write( "This may be an acceptable answer.

\n" ); document.write( "But we can go a little further. You might notice that since $\"sin%5E2%28theta%29+=+1+-+cos%5E2%28theta%29\"$ , the expression we have is the negative of $\"sin%5E2%28theta%29\"$ . If you don't notice this then you could use substitute $\"1-sin%5E2%28theta%29\"$ for $\"cos%5E2%28theta%29\"$ :
\n" ); document.write( " $\"%281-sin%5E2%28theta%29%29+-+1\"$
\n" ); document.write( "The 1's cancel, leaving
\n" ); document.write( " $\"-sin%5E2%28theta%29\"$

\n" ); document.write( "So
\n" ); document.write( " $\"cos%5E2%28theta%29-1%29\"$
\n" ); document.write( "might be good enough but
\n" ); document.write( " $\"-sin%5E2%28theta%29\"$
\n" ); document.write( "is even simpler. \n" ); document.write( "

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