Question

If secx +tanx = k, then show tha sinx = (k^2 - 1) / (k^2 + 1)

Answer 1

Here, sec x  = (k^2 +1)/2k.
 So, cos x = 2k/(k^2 +1).

Thus, from sin x = Sqrt(1 - (cos x)^2). we get the required answer.
 Either you can derive it from triangle also. whichever is suitable to you.