Answer:
DC = 10 cm
Explanation:
given a tangent and a secant drawn to the circle from an external point, then the square of the measure of the tangent is equal to the product of the secant's external part and the entire secant , that is
AC × AD = AB²
8(8 + x) = 12² = 144 ( divide both sides by 8 )
8 + x = 18 ( subtract 8 from both sides )
x = 10
that is DC is 10 cm