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homework help. How do I prove that this is an identity?
it says cos^4 times x, minus sin^4 times x=2cos^2 times x minus 1
I know I have to make one side equal to the other side, but I'm stuck. Please help!
2 Answers
- Your AnswerLv 67 years agoFavorite Answer
cos^4 x -- sin^4 x
= cos^4 x -- (1 -- cos^2 x)^2 because sin^2 x + cos^2 x = 1
= cos^4 x -- 1 + 2cos^2 x -- cos^4 x
= 2cos^2 x -- 1
- DWReadLv 77 years ago
If you mean cos⁴(x), that means (cosine of x) to the 4th power. It does NOT mean cos⁴ times x.
cos⁴ is meaningless without an argument.
