Equation of pair of tangents from the point (0,b) drawn to the circle x2+y2=16 is, (x2+y2−16)(b2−16)=(by+16)2 For point A and B, take y = 0, So, (x2−16)(b2−16)=162 x±
4b
√b2−16
Now, For ∆PAB, Δ=±
1
2
b(
8b
√b2−16
) =
4b2
√b2−16
For minimum area
dΔ
db
=0, √b2−16(8b)=4b2
b
√b2−16
b2=32 b=±4√2 So, P(0,±4√2),A(4√2,0) and B(−4√2,0) Thus, the equation of the circumference of ∆PAB is x2+y2=32