Answer:
15
Step-by-step explanation:
(whole secant) x (external part) = (tangent)^2
(5+x) * 5 = 10^2
Distribute
25 +5x = 100
Subtract 25 from each side
25-25 +5x = 100-25
5x= 75
Divide by 5
5x/5 = 75/5
x = 15
