document.write( "Question 604252: How do you prove that \"cos%285x%29+=+5+cos%28x%29+-+20+cos%5E3%28x%29+%2B+16+cos%5E5%28x%29\" using sum and difference identities? Thank you :D\r
\n" ); document.write( "\n" ); document.write( "*EDIT: I'm so sorry, cos^5 x should be cos 5x \n" ); document.write( "
Algebra.Com's Answer #381065 by jsmallt9(3758)\"\" \"About 
You can put this solution on YOUR website!
This cannot be correct because ...
  • What you posted was:
    \n" ); document.write( "\"cos%5E5%28x%29+=+5cos%28x%29+-+20cos%5E3%28x%29+%2B+16cos%5E5%28x%29\"
    \n" ); document.write( "This is not an identity. This equation is only true for certain values of x, not all values of x.; and
  • All the arguments are x. There is no need to use sum and/or difference identities to manipulate the arguments.

\n" ); document.write( "If you re-post the question, then I wonder if the double angle and half angle identities would be considered \"sum and difference identities\"? I ask because I suspect that they might be very helpful. \n" ); document.write( "
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