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

# Factor formula help C3 watch

1. Prove 1+2COS2X +COS4X = 4COS^2COS2X

Need help
2. bump
3. ..
5. (Original post by Mesosleepy)
Prove 1+2COS2X +COS4X = 4COS^2COS2X

Need help
How far did you get? What working do you have so far?
6. (Original post by Mesosleepy)
Prove 1+2COS2X +COS4X = 4COS^2COS2X

Need help
Starting from LHS, try simplifying Cos4x in terms of Cos2x (using the formula for Cos2x, but everything is multiplied by 2 I think).

The rest is basically further simplifying
7. I don't think its right but

1+2 [ cos2x +cos 4x ]
[ 2cos(2x+4x/2)cos(2x-4x/2)] = [2cos(3x)cos(-x)]
1+2 [2cos(3x)cos(x)] cos(x) because cos(-x) is same as cos(x)
1+4cos(3x)cos(x)
8. (Original post by kkboyk)
Starting from LHS, try simplifying Cos4x in terms of Cos2x (using the formula for Cos2x, but everything is multiplied by 2 I think).

The rest is basically further simplifying
Wait, so Cos4x becomes 2(Cos2x)
9. Nvm guys I found out how to do it

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: October 30, 2015
Today on TSR

### Negatives of studying at Oxbridge

What are the downsides?

### Grade 9 in GCSE English - AMA

Poll
Useful resources

Can you help? Study help unanswered threadsStudy Help rules and posting guidelinesLaTex guide for writing equations on TSR

## Groups associated with this forum:

View associated groups

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