# FP2 series help

Watch
Announcements
#1
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?
0
3 years ago
#2
Put cosx into its exponential form and then use the Maclaurin series for ex maybe?
0
3 years ago
#3
Or just use the generic formula of

where f(x) = ln(cosx), f'(x) = -tanx and f''(x) = -sec2 x
0
#4
(Original post by ashmcm)
Put cosx into its exponential form and then use the Maclaurin series for ex maybe?
How would I go about doing that
0
3 years ago
#5
(Original post by Carman3)
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?
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...
1
3 years ago
#6
there is an expansion for ln( 1 + x )

and the expansion of cos begins 1 - x2/2
0
#7
(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
0
3 years ago
#8
(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
Chain rule, differentiating ln(cosx) = 1/cosx * -sinx = -tanx
0
#9
Hm. I guess I used to do it differently in core 3 whether that may be wrong. Sorry if it was painfully obvious and thanks all for the help
0
X

new posts
Back
to top
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

### Poll

Join the discussion

#### Should there be a new university admissions system that ditches predicted grades?

No, I think predicted grades should still be used to make offers (639)
33.47%
Yes, I like the idea of applying to uni after I received my grades (PQA) (806)
42.22%
Yes, I like the idea of receiving offers only after I receive my grades (PQO) (378)
19.8%
I think there is a better option than the ones suggested (let us know in the thread!) (86)
4.5%