Cos A is negative in the 3rd quadrant and you found Cos 2A = 4/5. Where is Cos A positive? Don't forget your range for angle A.
Since Tan A = 1/3, that puts A in quadrant I or quadrant III because that's the only 2 quadrants where Tan A is positive.2. I need help with this one. Can someone explain to me how I would know which quadrant the angle 2A would be in? How to approach and answer this?
ArcTan A is about 18.4 degrees in quadrant I and 198.4 in quadrant III. Cos 2A would either be about 36.8 degrees in quadrant I or about 323.2 degrees in quadrant IV which is out of range.