Answer:
x = 6
Step-by-step explanation:
Tangent - Secant Power Theorem: 18^2 = 12(21 + x)
324 = 252 + 12x
72 = 12x
x=6
(whole secant) x (external part) = (tangent)^2
(12+x+9)*12 = 18^2
(21+x)12 =324
Divide each side by 12
(21+x) 12/12 = 324/12
21+x = 27
Subtract 21 from each side
21+x-21 =27-21
