You are Here: Home >< Maths

# FP2 Maclaurins/Taylors Watch

Announcements
1. Hi, I understand the basic method of this, but I'm confused on how to do it when there is a combined function
e.g. Expanding ln(sinx) in taylors using (x-pi/6).
I think you have to consider separaetly the expansion of lnx and sinx but I don't understand where to go from there. Any help appreciated thanks
2. Basically, imagine you have ln(u) instead of ln(x) and do the expansion in terms of u. I can't remember the series or I'd write it for you, but it's something like lnu = 1 - u + u^2 - u^3 + ... or whatever.

Then do the expansion for sinx

Now let u = sinx.

So whereever you see u in your expansion of lnu, replace it with the expansion of sinx. It's messy, but it works apparently. So you'll have something like

ln u = 1 - (sinx) + (sinx)^2 - (sinx)^3

But instead of writing sinx, you write the expansion of sinx.
3. and the expansion of sin x would be just up to the terms it's asked for e.g. to x^3? and then you expand it all out?
thank you by the way
4. (Original post by lilwhizzz)
and the expansion of sin x would be just up to the terms it's asked for e.g. to x^3? and then you expand it all out?
thank you by the way
Yeah, expand both up to the require term. Then when you plug sinx into the lnu, you'll get something like u^3 = (x + x^2 + x^3)^3, after expanding, you'll have x^9 as well, which you just have to leave out. Hence it gets messy!

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: December 27, 2010
Today on TSR

### Things NOT to do at uni

Have you done any of these?

### How much revision have yr12s done?

Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

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

• Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams

## Groups associated with this forum:

View associated groups
Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

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

• The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.