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    Hi,

    Use Maclaurin's theorem to obtain the first three non-zero terms in the expansion of f(x)= (e^x + e^-x)/2

    I got the answer of 1+x^2/2!+x^4/4!

    but apparently the answer is 2+x^2+x^4/12

    please help me through which parts I've gotten wrong

    Thanks!
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    Your answer is correct, they have forgotten to divide by 2.
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    As already said you are correct. Did you notice it is the expansion of coshx?
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    (Original post by Ewanclementson)
    Your answer is correct, they have forgotten to divide by 2.
    Thanks for your help!
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    (Original post by B_9710)
    As already said you are correct. Did you notice it is the expansion of coshx?
    no we haven't learned about cosh and other trigs
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    (Original post by liemluji)
    no we haven't learned about cosh and other trigs
    cosh = hyperbolic cosine, so it isn't a trig function. If you know about the unit circle definition of trig functions, then basically to get the hyperbolic trig functions you do the same sort of thing but with a hyperbola instead of a circle. You should learn about them in FP2.
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    (Original post by HapaxOromenon3)
    cosh = hyperbolic cosine, so it isn't a trig function. If you know about the unit circle definition of trig functions, then basically to get the hyperbolic trig functions you do the same sort of thing but with a hyperbola instead of a circle. You should learn about them in FP2.
    Depends on the exam board, it's covered in FP3 for Edexcel.
 
 
 
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