∫∠ABC = 90°
∴ab is the diameter of this circle.
In △pao and △pbo.
oa=ob,po=po,pa=pb
∴△pao≌△pbo(sss)
∴∠pao=∠pbo
∫pa is the tangent of the circle.
∴∠ pao = 90 degrees (tangent property)
∴∠ PBO = 90 (equivalent substitution)
Ob is the radius of the circle.
∴pb is the tangent of the circle.
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