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    If the first 3 terms in the expansion of ln(cosx+sinx) = x-x^2+(2/3)x^3
    How do you automatically know hat ln(cosx-sinx) = -x-x^2-(2/3)x^3
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    you can rewrite ln(cosx-sinx) as ln ( cos(-x) + sin( -x ) )

    because of the odd/even thing with sin & cos
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    (Original post by the bear)
    you can rewrite ln(cosx-sinx) as ln ( cos(-x) + sin( -x ) )

    because of the odd/even thing with sin & cos
    Of course. Seems so simple now. I just could not see it.
 
 
 
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Updated: October 22, 2015
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