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**iAlphaBeasti** If Sin X = -4/5 and X is in Quadrant 4, then find Cos 2X

I have used the Double Angle ID and I got -7/25 as my answer.

However, here is where my problem is at. The question says that X is in Q4, so therefore Cos has to be positive right?

This was a question that I did on my Trig test and I got it wrong...the choices were...

A. -24/25

B. -7/25

C. 24/25

D. 7/25

I chose D because Cos is positive in Q4, however the correct answer was B, the exact same answer I got when I used the double angle formula...but it says X is in Q4????

Can somebody explain this to me please? Thanks!