If two secants are drawn from a point lying outside a circle, then the product of one secant on its outer part is equal to the product of the other secant on its outer part.
DE*CE = AE*BE
DE = CD + CE = 1 + x + 4 = x + 5
AE = AB + BE = 11 + x + 1 = x + 12
(x+5)(x+4)=(x+12)(x+1)
x² + 4x + 5x + 20 = x² + x + 12x + 12
9x + 20 = 13x + 12
20 - 12 = 13x - 9x
8 = 4x
x = 8/4
x = 2
