# Thread: Cos2θ to sinθ? Identity conversions

1. ## Cos2θ to sinθ? Identity conversions

How to find cos2θ if sinθ = 2?

How to find cosθ if sin2θ = 3?

Both lie in quadrant I. I'm unsure how to convert from one identity to the other ...

2. ## Re: Cos2θ to sinθ? Identity conversions

How can $sin(\theta) = 2$ if its maximum value is 1.

3. ## Re: Cos2θ to sinθ? Identity conversions

In this post ...

Double Angle Equations!

...you were requested to post specific problems rather than cryptic references to double angle problems. Now it seems you're making up stuff, because you really don't know what you're doing.

Post a specific problem from a text or as given by your instructor.

4. ## Re: Cos2θ to sinθ? Identity conversions

Originally Posted by whittwhitt
How to find cos2θ if sinθ = 2?

How to find cosθ if sin2θ = 3?

Yes. Impossible. $-1 \leq sin(\theta) \leq 1$. For any angle in any quadrant.

Originally Posted by whittwhitt
I'm unsure how to convert from one identity to the other ...
You have now got several references to the double angle formulas. Please use them and show us what you've got.

But please let us know what the actual problem statements are. You have been asked to clarify a question before.

-Dan