Hi neeraj,

The circle is nothing but the 1 with diameter as TG and center at S(a,0) ;

Let the PTS =  ;{ where Tan  = 1 / t }

Let the angle bt tangents be  ;

So, ext angle PSG = { +( /2 - )}

Just expand..TanPSG  { = 2t / (t²-1) } ;

Solve for cot  ;{u get it as 1/t }

So,   = Tan^-1(1/t) ....ans.