C3 Trig Identities help! Watch

bobbricks
Badges: 17
Rep:
?
#1
Report Thread starter 5 years ago
#1
Solve in the range \pi<x<-\pi the equation \cos3x+\cos x=0

This is what I've done so far (using the factor formulae):
2\cos \frac{3x+x}{2} \cos \frac{3x-x}{2} =0

The next step is supposedly:
\cos2x\cos=0 but I'm not sure how to get there. Can someone help please?
0
reply
Kvothe the Arcane
  • Study Forum Helper
Badges: 20
Rep:
?
#2
Report 5 years ago
#2
(Original post by bobbricks)
Solve in the range \pi<x<-\pi the equation \cos3x+\cos x=0

This is what I've done so far (using the factor formulae):
2\cos \frac{3x+x}{2} \cos \frac{3x-x}{2} =0

The next step is supposedly:
\cos2x\cosx=0 but I'm not sure how to get there. Can someone help please?
What is \frac{3x+x}{2} and \frac{3x-x}{2}?
0
reply
bobbricks
Badges: 17
Rep:
?
#3
Report Thread starter 5 years ago
#3
(Original post by keromedic)
What is \frac{3x+x}{2} and \frac{3x-x}{2}?
It's one of the factor formulae/trig identities:
http://www.examsolutions.net/maths-r.../example-1.php

Not all exam boards cover it apparently (I'm on Edexcel)
0
reply
Kvothe the Arcane
  • Study Forum Helper
Badges: 20
Rep:
?
#4
Report 5 years ago
#4
(Original post by bobbricks)
It's one of the factor formulae/trig identities:
http://www.examsolutions.net/maths-r.../example-1.php

Not all exam boards cover it apparently (I'm on Edexcel)
I know what it is...
evaluate what I asked and the answer to your question should be obvious...
0
reply
bobbricks
Badges: 17
Rep:
?
#5
Report Thread starter 5 years ago
#5
(Original post by keromedic)
I know what it is...
evaluate what I asked and the answer to your question should be obvious...
But shouldn't it become
2\cos 2x \cos x =0 (with the 2 in front)?

Unless it was a typo in the worksheet..
0
reply
Kvothe the Arcane
  • Study Forum Helper
Badges: 20
Rep:
?
#6
Report 5 years ago
#6
(Original post by bobbricks)
But shouldn't it become
2\cos 2x \cos x =0 (with the 2 in front)?
the 2 at the front isn't important but yes, that's what it becomes. What's the question?
0
reply
bobbricks
Badges: 17
Rep:
?
#7
Report Thread starter 5 years ago
#7
Okay, I've managed to get it thanks
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

University open days

  • Arts University Bournemouth
    Art and Design Foundation Diploma Further education
    Sat, 25 May '19
  • SOAS University of London
    Postgraduate Open Day Postgraduate
    Wed, 29 May '19
  • University of Exeter
    Undergraduate Open Day - Penryn Campus Undergraduate
    Thu, 30 May '19

How did your AQA GCSE Physics Paper 1 go?

Loved the paper - Feeling positive (196)
30.2%
The paper was reasonable (263)
40.52%
Not feeling great about that exam... (110)
16.95%
It was TERRIBLE (80)
12.33%

Watched Threads

View All