Question 872831
If cot A = 4/3, with A in Q3, Find sec 2A.
You are working with a (3-4-5) reference right triangle in Q3 in which sin<0, cos<0
cos A=-4/5
sin A=-3/5
cos 2A=cos^2A-sin^2A=16/25-9/25=7/25
sec 2A=1/cos 2A=25/7
..
calculator check:
cos A=-4/5
A&#8776;216.87&#730;
2A&#8776;433.74
cos 2A&#8776;cos(433.74)&#8776;0.2799…
Exact value=7/25&#8776;0.28