Answer:
x = 5
Explanation:
Two secants from an external point to a circle, then the product of one secant's external part and the entire secant is equal to the product of the external part and the entire secant of the other, that is
(x - 2)(x - 2 + x + 4) = 4(4 + 5)
(x - 2)(2x + 2) = 4(9) = 36 ← distribute and simplify the left side
2x² + 2x - 4x - 4 = 36
2x² - 2x - 4 = 36 ( subtract 36 from both sides )
2x² - 2x - 40 = 0 ( divide through by 2 )
x² - x - 20 = 0 ← in standard form
(x - 5)(x + 4) = 0 ← in factored form
Equate each factor to zero and solve for x
x - 5 = 0 ⇒ x = 5
x + 4 = 0 ⇒ x = - 4
But x > 0 ⇒ x = 5