You are Here: Home >< Maths

# Trig question watch

1. Attachment 500069500071

I don't know how to find the right answer for cos (2theta) ?
Attached Images

2. Do you have a formula for cos(2A) in terms of sinA?

Usually called the double angle formula.

Spoiler:
Show
cos2A = 1 - 2sin^2(A)
3. (Original post by Airess3)

Attachment 500069500071

I don't know how to find the right answer for cos (2theta) ?
As the above user has suggested, you need to apply the double angle formula as, for example, .

### Related university courses

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: February 2, 2016
Today on TSR

### Edexcel GCSE Maths Unofficial Markscheme

Find out how you've done here

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