You are Here: Home >< Maths

# C3 Trig Help! watch

Announcements
1. sin2x = cos2x, solve for 0<x<2pi

i have tried rearranging and all i get is: 2sin^2x -2sinxcosx -1 = 0, and that doesn't factorise.

Please point me in the right direction

thanks (oh and rep on offer, altho it wont be worth much =P )
2. I'd put sin 2x - cos2x in R sin (2x + alpha ) form
3. I would divide both sides by cos 2x to give you tan 2x = 1, then solve from there?
4. 2sinxcosx = cos2x - sin2x

Divide through by cos2x

2tanx = 1 - tan2x

And make a quadratic out of that
5. (Original post by LetoKynes)
I would divide both sides by cos 2x to give you tan 2x = 1, then solve from there?
This.
6. ah cheers guys. you guys make c3 seem look so simple lol
7. Why didn't I see that
8. (Original post by Tommy Jay)
ah cheers guys. you guys make c3 seem look so simple lol
Trig is a nasty chapter, because even if you do understand it, you might not see the solution. What I've worked out when doing trig is that most of the time when proving something you should look out for these things.

-Sin and cos turning into tan
-sin^2 + cos^2 = 1
-1 + tan^2 = Sec^2
-1 + cos^2 = Cot^2
-Cos 2x giving cos^2 x-sin^2 x which is the difference of two squares, (cosx+sinx) (cosx-sinx)
-Then ofc just expanding sin 2x and cos 2x normally

Just look out for these in that order, they are usually the trickiest

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: January 31, 2010
Today on TSR

### Moving into halls?

How do unis decide who goes where?

### University open days

• University of Lincoln
Wed, 12 Dec '18
• Bournemouth University
Midwifery Open Day at Portsmouth Campus Undergraduate
Wed, 12 Dec '18
• Buckinghamshire New University
Wed, 12 Dec '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