Let XY be a tangent to a circle, and let XBA be a secant of the circle, as shown below. If AX = 16 and XY = 9, then what is AB?
By the tangent - secant theorem
XY^2 = AX * XB
9^2 = 16 * XB
81 = 16 * XB
81 / 16 = XB
So
BA = AX - XB
BA = 16 - 81/16
BA = (256 - 81) / 16
BA = 175 / 16
