Double Angle Question

[Guest]

If im given a value for a double angle, such as Cos 2A = 7/18, how do I find possible values of Sin A and Cos A?

 

[Mrspi]

If im given a value for a double angle, such as Cos 2A = 7/18, how do I find possible values of Sin A and Cos A?

cos 2A = 2 cos² A - 1

and

cos 2A = 1 - 2 sin² A


Substitute 7/18 for cos 2A, and solve for the possible values of sin A and cos A.