Use Pythagorean Theorem: a² + b² = c² "a" is one side of the right triangle. Its length is: radius of larger circle minus radius of smaller circle: (11 - 3 = 8) The distance between the center of the circles creates the hypotenuse (17) 8² + b² = 17² b² = 225 b = 15
Answer: the length of the common external tangent is 15.
