Circles: The Length of Tangent/Secant Lines Endpoint outside the circle…

Secant and Tangent Lines If part of secant line is outside circle, call it the “external segment.” A DA = Secant Line DC = Tangent Line DB = External Segment of the Secant Line. B D C

Secant and Tangent Lines The square of the tangent line is equal to the product of the external segment and the whole secant line. (Tangent)2 = External Segment(Secant Line) A (DC)2 = DB(DA) B D C

Example 8 x Secant: DA = 20 Ext. Seg: DB = 8 (DC)2 = DB(DA) To find an unknown length: Use a variable. Substitute the values you know. Simplify. Secant: DA = 20 Ext. Seg: DB = 8 A (DC)2 = DB(DA) B 8 (x)2 = 8(20) D x C