You are Here: Home >< Maths

# Solve -2/3cot(2x)=0 Help Watch

1. (Original post by Alisahussain1)
im sorry but that makes no sense to me at all but as long as you understand it thats fine with me
What don't you understand?
2. (Original post by Zacken)
What don't you understand?
wait i think i know what youre talking about!!
but i dont get the exact same answers as i did before because i get pi/4 and 7pi/4??
3. (Original post by Alisahussain1)
wait i think i know what youre talking about!!
but i dont get the exact same answers as i did before because i get pi/4 and 7pi/4??
How do you get that?

cos 2x = 0 when 2x = pi/2 or 3pi/2

So x = pi/4 or 3pi/4.
4. (Original post by Zacken)
What don't you understand?
i got

cos2x=0
2cos^2x-1=0
cos^2x=1/2
cosx= sqrt(1/2)
cosx=plus or minus 1/2
x=pi/4 and 7pi/4
5. (Original post by Zacken)
How do you get that?

cos 2x = 0 when 2x = pi/2 or 3pi/2

So x = pi/4 or 3pi/4.
ohhh you just substituted random numbers in until you got 0, i see
6. (Original post by Alisahussain1)
ohhh you just substituted random numbers in until you got 0, i see
...what? No, not at all...
7. (Original post by Zacken)
...what? No, not at all...
LOL dont worry, as long as i got it right im not to bothered haha
8. (Original post by Alisahussain1)
LOL dont worry, as long as i got it right im not to bothered haha
But this is a worrying gap in your knowledge, surely?

Set y = 2x

then you have cos y = 0

Solve cos y = 0.

Then y = pi/2, 3pi/2, yes?

Now replace y with 2x again.

So 2x = pi/2 or 2x = 3pi/2, yes?

Now solve for x by dividing both sides.
9. (Original post by Zacken)
But this is a worrying gap in your knowledge, surely?

Set y = 2x

then you have cos y = 0

Solve cos y = 0.

Then y = pi/2, 3pi/2, yes?

Now replace y with 2x again.

So 2x = pi/2 or 2x = 3pi/2, yes?

Now solve for x by dividing both sides.
ohhhh i get itt!!! thank you! i just made a calculation error when i was putting the numbers in the calculator lol
10. (Original post by Alisahussain1)
ohhhh i get itt!!! thank you! i just made a calculation error when i was putting the numbers in the calculator lol
Cool.

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: June 10, 2016
Today on TSR

### Last-minute PS help

100s of personal statements examples here

### More pressure for kinky sex?

Discussions on TSR

• Latest
• ## 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.

• Poll
Useful resources

## Make your revision easier

### 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

Can you help? Study help unanswered threads

## Groups associated with this forum:

View associated groups
Discussions on TSR

• Latest
• ## 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.

• The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.