You are Here: Home >< Maths

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

Announcements Posted on
TSR's new app is coming! Sign up here to try it first >> 17-10-2016
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.

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

Updated: June 10, 2016
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:
Today on TSR

### How does exam reform affect you?

From GCSE to A level, it's all changing

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read here first

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams