(Geometry) Circle, angles and tangents problem Let P be an external point of a circle with center in O and also the intersection of two lines r and s that are tangent to the circle. If PAB is a triangle such that AB is also also tangent to the circle, find AÔB knowing that P = 40°.
I draw the problem:

Then I tried to solve it, found some relations, but don't know how to proceed.

I highly suspect that PAB is isosceles, but couldn't prove it.

We know $\angle PON=70°$ and $\angle NOP=140°$.
And we also know that $OB$ and $OA$ are bisectors of $\angle NOT$ and $\angle TOM$ respectively. Therefore $$BOT+TOA=70°$$

