- #1

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This is exercise set 3.3, problem 63.

cos^2(x) - 2sin^2(x)cos^2(x) - sin^2(x) + 2sin^4(x) = cos^2(2x)

Can anyone figure this out, or is this a misprint?

Thanks for your help,

Joe

- Thread starter jtart2
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- #1

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This is exercise set 3.3, problem 63.

cos^2(x) - 2sin^2(x)cos^2(x) - sin^2(x) + 2sin^4(x) = cos^2(2x)

Can anyone figure this out, or is this a misprint?

Thanks for your help,

Joe

- #2

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Have you tried using the double angle formulae for cosine to expand the right hand side?

- #3

uart

Science Advisor

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No Joe, it works out ok.Can anyone figure this out, or is this a misprint?

Start with [itex]cos^2 x - sin^2 x = cos 2x[/itex] and square both sides. This gets you the require RHS straight up and most of the terms you require on the LHS too. You then need to do a bit more work (apply more trig identities to the terms that don't yet "fit") on the LHS and it comes out fairly easily.

- #4

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Joe

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