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# Maclaurin's theorem help!!

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1. 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

Thanks!
2. Your answer is correct, they have forgotten to divide by 2.
3. As already said you are correct. Did you notice it is the expansion of coshx?
4. (Original post by Ewanclementson)
5. (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
6. (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.
7. (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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