Answer:
DF = 9.5
Explanation:
Given 2 secants from an external point to the circle, then
The product of the external part and the whole of one secant is equal to the product of the external part and the whole of the other secant, that is
DE × DF = DC × DB
5(5 + x) = 5(5 + 4.5) ← divide both sides by 5
5 + x = 5 + 4.5
5 + x = 9.5 ( subtract 5 from both sides )
x = 4.5
Then
DF = DE + EF = 5 + 4.5 = 9.5