Sunday, December 7, 2008

Common chord of two circles

Equation
2x(g1-g2)+2y(f1-f2)+c1-c2 = 0

This is for circles

Circle 1 (termed as S1) x² + y²+2g1x+2f1y+c = 0

Circle 2 (termed as S2) x² + y²+2g2x+2f2y+c = 0

Length of the common chord = 2√ (C1P²-C1M²)
Where
C1P = radius of circle 1
C1M = length of the perpendicular from the centre C1 to the common chord PQ.

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