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Chord of Contact from an External Point
For circle:
$$x^2+y^2+2gx+2fy+c=0$$
the chord of contact from $$(x_1,y_1)$$ is:
$$xx_1+yy_1+g(x+x_1)+f(y+y_1)+c=0$$
Usage
- Used to find the line joining the two points of contact of tangents drawn from an external point.
