You are Here: Home >< Maths

# c3 trig query ( can i re-arrange like this.....) watch

1. I have an equation: cosecx - 8cosx = 0

and I have to solve it, 0 < x < pi

can I change it to: 1/sinx - 8cosx/sinx = 0

then get: 1/sinx = 8cosx/sinx

then: 1 = 8cosxsinx/sinx

then: 1 = 8cosx

is this all right????? if not, how do I re-arrange the equation to solve it?
2. (Original post by W.H.T)
I have an equation: cosecx - 8cosx = 0

and I have to solve it, 0 < x < pi

can I change it to: 1/sinx - 8cosx/sinx = 0

then get: 1/sinx = 8cosx/sinx

then: 1 = 8cosxsinx/sinx

then: 1 = 8cosx

is this all right????? if not, how do I re-arrange the equation to solve it?
either you posted the question incorrectly or your working is incorrect
3. (Original post by W.H.T)
I have an equation: cosecx - 8cosx = 0

and I have to solve it, 0 < x < pi

can I change it to: 1/sinx - 8cosx/sinx = 0

then get: 1/sinx = 8cosx/sinx

then: 1 = 8cosxsinx/sinx

then: 1 = 8cosx

is this all right????? if not, how do I re-arrange the equation to solve it?
No, you can't put 8cosx over sinx
I haven't looked into it, but I'd suggest trying to get it in terms of tan, or trying to cancel out either sin or cos....
4. Consider this

multiply by sin(x) to get

now consider using the identity

5. can I do this instead:

cosecx - 8cosx = 0

1/sinx - 8cosx = 0

1/sinx = 8cosx

1 = 8cosxsinx

1 = 4sin2x <------- double angle formulae

1/4 = sin2x
Consider this

multiply by sin(x) to get

now consider using the identity

thank you, can you check my post above that its all correct
7. (Original post by Pheylan)
either you posted the question incorrectly or your working is incorrect
well thats narrowed it down.
8. Yeah thats looking good to me! I get x = 0.126 + 2n*pi from that

### Related university courses

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: January 18, 2010
Today on TSR

### Top unis in Clearing

Tons of places at all these high-ranking unis

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