Question 872831: If cot A = 4/3, with A in Q3, Find sec 2A.
Answer by lwsshak3(11628)   (Show Source):
You can put this solution on YOUR website! 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≈216.87˚
2A≈433.74
cos 2A≈cos(433.74)≈0.2799…
Exact value=7/25≈0.28
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