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FP2 series help

In the book there's a question which says find the maclaurins series for lncosx using differentiation and I'm finding it difficult to do I searched Google for a way on how to do it but it seems something beyond a level?

Reply 1

ashmcm

Put cosx into its exponential form and then use the Maclaurin series for e^x maybe?

Reply 2

ashmcm

Or just use the generic formula of

where f(x) = ln(cosx), f'(x) = -tanx and f''(x) = -sec² x

Reply 3

Carman3

Original post by ashmcm

Put cosx into its exponential form and then use the Maclaurin series for e^x maybe?

How would I go about doing that

Reply 4

davros

Original post by Carman3

What are you finding difficult? Presumably you know what the definition of a Maclaurin series is, and how to find the coefficients by repeated differentiation...

Reply 5

the bear

there is an expansion for ln( 1 + x )

and the expansion of cos begins 1 - x²/2

Reply 6

Carman3

Original post by davros

What are you finding difficult? Presumably you know what the definition of a Maclaurin series is, and how to find the coefficients by repeated differentiation...

If I let f (x) = lncosx, how do I find f'(x). The question says use differentiation so I have to find f (x)

Perhaps u shouldve been more exact on what I needed help with

Reply 7

ashmcm

Original post by Carman3

If I let f (x) = lncosx, how do I find f'(x). The question says use differentiation so I have to find f (x)

Perhaps u shouldve been more exact on what I needed help with