Posted by **please help me out!!! please** on Monday, February 11, 2013 at 10:53am.

Let O be the center of the circle Γ, and P be a point outside of circle Γ. PA is tangential to Γ at A, and PO intersects Γ at D. If PD=14 and PA=42, what is the radius of Γ.

- geometry -
**Reiny**, Monday, February 11, 2013 at 11:27am
In this case the secant - tangent theorem says

PA^2 = PD x PC , where D in on the extension of PO as it hits the circle , making CD a diameter

Let the diameter be 2x , (radius = x)

(14)(2x+14) = 42^2

28x + 196 = 1764

28x = 1568

x = 56

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