Tangents from the external point are equal in length.
Proof:
Let PA and PB be the tangents to the circle O.
Join OP
∠OAP = ∠OBP = 90° tangent is perpendicular to radius
ΔOAP and PBPΔ are right triangle
ΔOAP ≅ ΔOBP Hypotenuse Leg Theorem
OA=OB = r circle property
OP, hypotenuse is common
AP = BP Congruent triangles
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