You are Here: Home >< Maths

# Trig mk8 Watch

1. -180°≤x≤180°
5sin²x=4cos²x

i went with the route of making 5sin²x into 5(1-cos²x)

i got cosx=0.68 and -1.47

x=±47.4° which is right but again i'm missing 2 other answers
2. (Original post by thefatone)
-180°≤x≤180°
5sin²x=4cos²x

i went with the route of making 5sin²x into 5(1-cos²x)

i got cosx=0.68 and -1.47

x=±47.4° which is right but again i'm missing 2 other answers
as before ... plus or minus ...
3. (Original post by TeeEm)
as before ... plus or minus ...

5cos²x+4cosx-5=0
let cosx=y
5y²+4y-5
4. (Original post by thefatone)
-180°≤x≤180°
5sin²x=4cos²x

i went with the route of making 5sin²x into 5(1-cos²x)

i got cosx=0.68 and -1.47

x=±47.4° which is right but again i'm missing 2 other answers
Looks like you solved the quadratic wrong, you should have gotten , mind posting your working for the quadratic solving part?
5. (Original post by thefatone)
-180°≤x≤180°
5sin²x=4cos²x
(Original post by thefatone)

5cos²x+4cosx-5=0
let cosx=y
5y²+4y-5
Where did the square go?
6. (Original post by Zacken)
Where did the square go?
ah that's where i went wrong....
7. (Original post by thefatone)
ah that's where i went wrong....
Yep.
8. thanks a bunch guys

everytime it's something little >.>
9. (Original post by thefatone)
-180°≤x≤180°
5sin²x=4cos²x

i went with the route of making 5sin²x into 5(1-cos²x)

i got cosx=0.68 and -1.47

x=±47.4° which is right but again i'm missing 2 other answers
Seems easier in this case to rearrange to get
.
10. (Original post by B_9710)
Seems easier in this case to rearrange to get
.
good point i could've done that aswell, that woulda been easier actually...

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: February 20, 2016
Today on TSR

### Anxious about my Oxford offer

What should I do?

### 3 unconditional offers - can't decide!

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

### 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

## 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