A tangent intersects a circle in exactly one place. It is a line which touches a circle or ellipse at just one point. The square of the length of tangent segment equals to the difference of the square of length of the radius and square of the distance between circle center and exterior point. Length of the tangent from a point can be calculated from circle radius and distance between exterior point and center using this online Tangent of a Circle Calculator.
A circle has distance between Exterior Point and its Center as 12cm and radius as 7cm.
Length of Tangent =√ 122 - 72 = √144 - 49
= 9.7468 cm