Equation of circle: x^2 +8x +y^2 -9 = 0Completing the square: (x+4)^2 +y^2 = 25Radius of circle: 5Center of circle: (-4, 0)Distance from (9, 0) to (-4, 0) = 13 which is the hypotenuse ofa right angle triangleUsing Pythagoras: 13^2 -5^2 = 144 and its square root is 12Therefore the length of the tangent line is 12 unitsNote that the tangent line of a circle meets the radius of thecircle at right angles