Let (x1,y1) be one of the points of tangency. Show that the equation of the tangent line through this point is x1(x) + y1(y) = R^2

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- Nov 25th 2013, 10:53 AMnycmathEquation of Tangent Line Through Point
Let (x1,y1) be one of the points of tangency. Show that the equation of the tangent line through this point is x1(x) + y1(y) = R^2

See picture. - Nov 25th 2013, 11:08 AMemakarovRe: Equation of Tangent Line Through Point
(x, y) is on the tangent iff (x, y) - (x1, y1) is perpendicular to (x1, y1). Express this condition using dot product.