Question 1089042
tan^2(A) = Sec^2(A) - 1 (Pythagorean's Theorem)

So Sec^2(A) - 1 = 3(Sec(A) - 1)

let u= Sec(A)

 u^2 - 3u + 2 = 0
 (u - 2)(u - 1) = 0

so u={1,2}

Sec(A) = 1 or Sec(A) = 2

A = 0 + 2k1*Pi = 2k1*Pi or (A = Pi/3 + 2k2*Pi or A =5Pi/3 + 2k3*Pi) , with k1,k2,k3 Integer

@natolino_