express the trig. ratios sinA,secA n
tanA in terms of cotA.
tan A = 1/cotA
1/cotA^2 = sin^2A/cos^2A
= (1 - cos^2A)/cos^2A
= [1/cos^2A] - 1
1 + (1/cot^2A) = 1/cos^2A
sec^2A = 1 + (1/cot^2A)
The sign of secA will depend upon the quadrant A is in