You are Here: Home >< Maths

# Proving a trigonometric identity watch

1. I'm trying to prove that
Sin(3x)=3sin(x) - 4sin^3(x)
My teachers first step is to write this
Sin(3x)= sin(2x+x)
Where does the sin(2x+x) come from?
2. (Original post by K622338)
I'm trying to prove that
Sin(3x)=3sin(x) - 4sin^3(x)
My teachers first step is to write this
Sin(3x)= sin(2x+x)
Where does the sin(2x+x) come from?
Never mind I get she factorised sin(3x)
3. You're just rewriting a 3x as 2x+x which then allows you to use trigonometric identities

### 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: March 10, 2018
Today on TSR

### He lied about his age

Thought he was 19... really he's 14

### University open days

Wed, 25 Jul '18
2. University of Buckingham
Wed, 25 Jul '18
3. Bournemouth University
Wed, 1 Aug '18
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