From an outside point P, Two tangents, PA and PB, are drawn to a circle. A third tangent to the circle at a point Q intersects PA and PB at R and s respectively. If PA = 10 cm, What is the perimeter of $\delta Prs$?

Given:
PA = 10 cm

Property: From an external point, tangents to a circle are equal.
So, PA = PB = 10 cm

Now, the third tangent at $Q meets PA at R and PB at S.

Using tangent properties:
RQ = R A and SQ = SB

Also, the total lengths split such that:
PR + RA = PA = 10
PS + SB = PB = 10

Adding:
PR + PS + (RA + SB) = 20

But RA + SB = RS (along the tangent structure)

So, perimeter of $\triangle PRS$:
$PR + RS + PS = 20$

Final Answer:

20 cm