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Tangent conditions between line and circumference


Given a circle and a point P(x, y) of the plan, we have:

a) if P belongs to the circumference, so there is a single line tangent to the circumference by P.

b) if P is outside the circumference, so there are two lines tangent to it by P.

c) if P is inside the circumference, so there is no tangent line to the circumference passing through the point P.

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