Hey there! Sign in to join this conversationNew here? Join for free
 You are Here: Home >< Maths

# c4 help watch

1. find the values of x in the range 0degrees < or equal to x < or equal 360 degrees. that satisfy sec(2x)=3

no idea what to do :/
2. (Original post by iamgreatness)
find the values of x in the range 0degrees < or equal to x < or equal 360 degrees. that satisfy sec(2x)-3

no idea what to do :/
sec(2x)-3 is an expression and expressions don't have solutions.

You've missed something out of your question.
3. (Original post by notnek)
sec(2x)-3 is an expression and expressions don't have solutions.

You've missed something out of your question.
im sorry its =3
4. (Original post by iamgreatness)
find the values of x in the range 0degrees < or equal to x < or equal 360 degrees. that satisfy sec(2x)=3

no idea what to do :/

so you can manipulate the equation to give

Can you continue from here? If not, post your working/ideas.
5. (Original post by notnek)

so you can manipulate the equation to give

Can you continue from here? If not, post your working/ideas.
i cant do it
6. (Original post by iamgreatness)
i cant do it
You don't know how to solve the equation between 0 and 360 degrees?

Could you solve between 0 and 720 degrees?

If so make a substitution .
7. (Original post by iamgreatness)
i cant do it
How would you solve ?

Do the same for this but here you'll have '2x =' intead of 'x ='.

Again, post any working and any ideas that you have if you're still stuck. This is not a solutions forum and it's hard to help if I don't know your problem.
8. (Original post by Mr M)
You don't know how to solve the equation between 0 and 360 degrees?

Could you solve between 0 and 720 degrees?

If so make a substitution .
or have no solution

because
9. (Original post by ztibor)
...
Well yes, we both know that was a typo.
10. (Original post by notnek)
How would you solve ?

Do the same for this but here you'll have '2x =' intead of 'x ='.

Again, post any working and any ideas that you have if you're still stuck. This is not a solutions forum and it's hard to help if I don't know your problem.
(Original post by Mr M)
You don't know how to solve the equation between 0 and 360 degrees?

Could you solve between 0 and 720 degrees?

If so make a substitution .
im sorry i cant do it

what bit is this whats it called i will look it up in my textbook but does it have a name e.g partial fracitons
11. (Original post by iamgreatness)
im sorry i cant do it

what bit is this whats it called i will look it up in my textbook but does it have a name e.g partial fracitons
This is just Core 2 trigonometry. You really should know it inside out by the time you study Core 4.
12. (Original post by iamgreatness)
find the values of x in the range 0degrees < or equal to x < or equal 360 degrees. that satisfy sec(2x)=3

no idea what to do :/
sec(2x) = 3

=> 1/cos(2x) = 3

=> cos(2x) = 1/3

click to magnify

Coordinate system contains the graphs of cos(2x) and 1/3, you can see they meet 4 times in the interval 0 to 360 degrees. So you are looking for 4 solutions.

Now use the inverse cosine (cos-1) function on your calculator to find one of the solutions.

Solution 1
cos-1(1/3) = 70.529 degrees

2x = 70.529 degrees

x = 35.264 degrees

Solution 2
Because of symmetri on the graph, solution 2 must be 180 degrees minus solution 1, solution 3 is 180 plus solution 1 and solution 4 is 360 minus solution1. (Use unit-circle to clarify this to yourself if coordinatsystem doesn't make sense)

x = 180 - 35.264 = 144.736 degrees

Solution 3

x = 180 + 35.264 = 215.264 degrees

Solution 4

x = 360 - 35.264 = 324.736 degrees
13. (Original post by Mr M)
This is just Core 2 trigonometry. You really should know it inside out by the time you study Core 4.
i got a B in c2, duno why this is in c4 section A examples then
14. (Original post by Studentdk)
...
Full solutions are not allowed in this forum. Please read the posting guide before making another post.
15. (Original post by iamgreatness)
i got a B in c2, duno why this is in c4 section A examples then
Because of the use of the reciprocal trigonometric ratio.
16. (Original post by iamgreatness)
i got a B in c2, duno why this is in c4 section A examples then
Do you understand what to do now?

I don't believe that you had literally no idea how to solve in that region.

To find one solution would be a GCSE question.
17. (Original post by notnek)
Do you understand what to do now?

I don't believe that you had literally no idea how to solve in that region.

To find one solution would be a GCSE question.
=> 1/cos(2x) = 3

=> cos(2x) = 1/3

it was just this step i had trouble with. i guess u just flip over the 1/cox(2x) to get cos2x and coz u flipped that u have to flip the 3 which makes 1/3??
18. (Original post by Studentdk)
sec(2x) = 3

=> 1/cos(2x) = 3

=> cos(2x) = 1/3

click to magnify

Coordinate system contains the graphs of cos(2x) and 1/3, you can see they meet 4 times in the interval 0 to 360 degrees. So you are looking for 4 solutions.

Now use the inverse cosine (cos-1) function on your calculator to find one of the solutions.

Solution 1
cos-1(1/3) = 70.529 degrees

2x = 70.529 degrees

x = 35.264 degrees

Solution 2
Because of symmetri on the graph, solution 2 must be 180 degrees minus solution 1, solution 3 is 180 plus solution 1 and solution 4 is 360 minus solution1. (Use unit-circle to clarify this to yourself if coordinatsystem doesn't make sense)

x = 180 - 35.264 = 144.736 degrees

Solution 3

x = 180 + 35.264 = 215.264 degrees

Solution 4

x = 360 - 35.264 = 324.736 degrees
thnx altho ur not supposed to post full solutions sometimes, like arnold scwarzeneger said, u have to bend rules. thank u
19. (Original post by notnek)
Full solutions are not allowed in this forum. Please read the posting guide before making another post.
I apologise for having gone against the common spirit of this forum by posting a full solution, I was not aware of this "rule".

I do however believe that the person asking the question had received so many hints without understanding, that at some point the best help would be to see a solution.
20. (Original post by iamgreatness)
=> 1/cos(2x) = 3

=> cos(2x) = 1/3

it was just this step i had trouble with. i guess u just flip over the 1/cox(2x) to get cos2x and coz u flipped that u have to flip the 3 which makes 1/3??
You should have mentioned this before.

Reply
Submit reply
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: March 30, 2013
Today on TSR

### Struggling to get going with your revision?

Get going with the all day revision thread

### Uni strikes! How do they affect you?

Discussions on TSR

• Latest
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

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

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