Let $\overline{XY}$ be a tangent to a circle, and let $\overline{XBA}$ be a secant of the circle, as shown below. If $XY = 8$ and $XB = BY = 10$, then what is the radius of the circle?
Impossible
Tangent - Secant Theorem
XY^2 = XB ( XB + BA)
8^2 = 10 (10 + BA)
64 = 100 + 10BA
-36 = 10BA
BA -36/10 = = -3.6 (BA is a distance and must be positive)
+400 
