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# Help with finding solutions in trig?

Maths and statistics discussion, revision, exam and homework help.

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1. Help with finding solutions in trig?
Hi, just revising trig identities and everything for C4. I'm doing fine at getting nearly the end, I'm just confusing myself with finding the actual solutions.

If for example I get cosx=1/2, I'm perfectly able to find the solutions to be 60 and 300 using CAST.

But how do you find the solutions if its negative for example, like cosx=-3/4 ?

I've had a bunch of different teachers and they've all said something different and how and how not to do it, so I'm just really confused.

Any method or rule to find the solutions in examples like this would be great.
2. Re: Help with finding solutions in trig?
Same rule

In your e.g. you did arccos(0.5) = 60, then did 360-60 = 300

Do exactly the same with -0.75 to get 139 and 221
3. Re: Help with finding solutions in trig?
(Original post by Amy-Rose)
Hi, just revising trig identities and everything for C4. I'm doing fine at getting nearly the end, I'm just confusing myself with finding the actual solutions.

If for example I get cosx=1/2, I'm perfectly able to find the solutions to be 60 and 300 using CAST.

But how do you find the solutions if its negative for example, like cosx=-3/4 ?

I've had a bunch of different teachers and they've all said something different and how and how not to do it, so I'm just really confused.

Any method or rule to find the solutions in examples like this would be great.
Have a look at this video.
4. Re: Help with finding solutions in trig?
if your using the CAST method - the trick is to do as if positive and then choose the 2 opposite CAST sections to to ones you would normally take for that function : )

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Last updated: June 1, 2012
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