x Turn on thread page Beta
 You are Here: Home >< Maths

# FP2 Prove by induction... watch

1. FP2 Jan 07 AQA Q7 for anyone interested!
Right, I have (cosx+isinx)n=cosnx+isinnx
I assume n=k and it works for n=1.
The problem is I cant make the sides equal for n=k+1
So far I have...
(Cosx+isinx)k+1
=(coskx+isinkx)(cosx+isinx)
Which is correct in the mark scheme, then you multiply out and the final answer must be cos(k+1)x+isin(k+1)x.
My problem is when multiplying out, how do I make this work.
Does coskxisinx+isinkxcosx cancel out somehow or equal zero somehow? So confused!
Thank you
2. (Original post by ChappersBC)
FP2 Jan 07 AQA Q7 for anyone interested!
Right, I have (cosx+isinx)n=cosnx+isinnx
I assume n=k and it works for n=1.
The problem is I cant make the sides equal for n=k+1
So far I have...
(Cosx+isinx)k+1
=(coskx+isinkx)(cosx+isinx)
Which is correct in the mark scheme, then you multiply out and the final answer must be cos(k+1)x+isin(k+1)x.
My problem is when multiplying out, how do I make this work.
Does coskxisinx+isinkxcosx cancel out somehow or equal zero somehow? So confused!
Thank you
3. (Original post by Clarity Incognito)
Oh my days! Your right, I can not believe I missed that. Thank you very much

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: March 23, 2011
Today on TSR

### Loughborough better than Cambridge

Loughborough at number one

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