HE is the tangent АH is the radius A tangent line to a circle is perpendicular to the radius drawn to the tangent point ⇒ m∠АHE = 90° ⇒ ΔАHE is the right triangle.
By the Pythagorean theorem: HE² = АE² - AH² HE² = 13² - 5² = 169 - 25 = 144 HE = √144 = 12 units .
