You are Here: Home >< Maths

# C3 Trig watch

1. Struggling with trig again can anyone help me
2. This is the transition I don't understand
3. first step you flip both sides of the equation then in the next step you mutiply the top and bottom of the fraction by (secθ -tanθ)
4. (Original post by Alex621)
first step you flip both sides of the equation then in the next step you mutiply the top and bottom of the fraction by (secθ -tanθ)
Why would you multiply by secθ -tanθ?

Posted from TSR Mobile
5. (Original post by Abby5001)
Why would you multiply by secθ -tanθ?

Posted from TSR Mobile
to perform the transition...

Posted from TSR Mobile
6. (Original post by Abby5001)
Why would you multiply by secθ -tanθ?

Posted from TSR Mobile
If you then expand the brackets you'll be able to use a trig identity to simplify the fraction
7. (Original post by Alex621)
If you then expand the brackets you'll be able to use a trig identity to simplify the fraction
Do you mind explaining in a bit more detail please step by step?

Posted from TSR Mobile
8. (Original post by Abby5001)
Do you mind explaining in a bit more detail please step by step?

Posted from TSR Mobile
Once you get to 1/x = (secθ -tanθ) / (secθ + tanθ) (secθ - tanθ)

Expand (secθ + tanθ) (secθ - tanθ), to get sec2θ - tan2θ.

Now use the identity sec2θ = tan2θ + 1, to simplify it
9. (Original post by Alex621)
Once you get to 1/x = (secθ -tanθ) / (secθ + tanθ) (secθ - tanθ)

Expand (secθ + tanθ) (secθ - tanθ), to get sec2θ - tan2θ.

Now use the identity sec2θ = tan2θ + 1, to simplify it
Sorry I wasn't clear, I just meant can you explain how you get to 1/x = (secθ -tanθ) / (secθ + tanθ) (secθ - tanθ)

Posted from TSR Mobile
10. (Original post by Abby5001)
Do you mind explaining in a bit more detail please step by step?

Posted from TSR Mobile
You are trying to get the difference of two squares on the denominator.

It's a bit like rationalising the denominator when you multiply by the conjugate.
11. (Original post by Muttley79)
You are trying to get the difference of two squares on the denominator.

It's a bit like rationalising the denominator when you multiply by the conjugate.
Right I think I see it's just that I would never think to do this in an exam so it's quite confusing but thank-you

Posted from TSR Mobile
12. (Original post by Abby5001)
Right I think I see it's just that I would never think to do this in an exam so it's quite confusing but thank-you

Posted from TSR Mobile

I used to hate trig questions in c3 because I never knew where to start but once you've looked at lots of questions you start to get an idea of what you need to do
13. (Original post by Alex621)
I used to hate trig questions in c3 because I never knew where to start but once you've looked at lots of questions you start to get an idea of what you need to do
That's good to know, so is multiplying by the conjugate something that is prevalent in c3 because I have never seen it aside from in surds?

Posted from TSR Mobile
14. (Original post by Abby5001)
That's good to know, so is multiplying by the conjugate something that is prevalent in c3 because I have never seen it aside from in surds?

Posted from TSR Mobile
I've never seen it before apart from surds but maybe different exam boards use it with trig?
15. (Original post by Abby5001)
Right I think I see it's just that I would never think to do this in an exam so it's quite confusing but thank-you

Posted from TSR Mobile
I think I've done this question recently - the method the markscheme used seem a little convoluted to me, I much prefer what I did!

and the continue from there converting everything into sines and cosines, collecting and then seperating and converting back to secs. (x + 1/x = 2 sec theta, right?)

### 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: September 18, 2015
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