Find Cos2X, Sin2X, Tan2X. If CosX=-3 and TanX

Question

Find Cos2X, Sin2X, Tan2X. If CosX=-3 and TanX<0

parthkohli · Answer

$$\cos(2x) = 1- 2\cos^2 x$$

parthkohli · Answer

Wait, how is $\cos(x) = -3$...?

anonymous · Answer

It was stated in the question. CosX=-3 and tanX is negative

parthkohli · Answer

As we all know, $-1 \le \cos x \le 1$.

@satellite73 Add another one to the list...

anonymous · Answer

I assume it just means that this lies in the second quadrant? if cosX is negative and tan is negative.

parthkohli · Answer

What I mean is that $\cos(x)$ can never be -3. Never, ever, ever, ever. 
How can the base be three times the hypotenuse in magnitude? Isn't the hypotenuse supposed to have the biggest magnitude?

anonymous · Answer

I guess this is a confusing question. its straight from my textbook though. So not sure what to say. I definitely have a 1 for my hypotenuse so far.