AO = 21 BC = 14 OC = radius of the circle = AO = 21 ∴ OB = OC + CB = 21 + 14 = 35 <span>Line AB is tangent to circle O at A</span> ∴ AB is perpendicular to AO ∴ Δ OAB is a right triangle at A Applying Pythagorean theorem ∴ OB² = AO² + AB² ∴ AB² = OB² - AO² = 35² - 21² = 1225 - 441 = 784 ∴ AB = √784 = 28 <span />
