Answer:
x = 3
Explanation:
Given two secants drawn 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
x(x + 21) = (x + 1)(x + 1 + 14)
x² + 21x = (x + 1)(x + 15) ← expand using FOIL
x² + 21x = x² + 16x + 15 ( subtract x² + 16x from both sides )
5x = 15 ( divide both sides by 5 )
x = 3