What is the value of x?

i know the answer is 2 but i need a explanation as to how to get that

When 2 secants intersect a circle:
(DC + CE) * CE = (AB + BE) * BE

( 1 + (x+4)) * (x+4) = (11 + (x+1)) * (x+1)

x + x^2 + 4x + 4 +4x +16 = 11x +x^2 +x +11 +x +1

9x + 20 = 13x + 12

4x = 8

x = 2

Source:
http://www.1728.org/circangl.htm
Scroll down to Two Intersecting Secants

Gee - that was a little bit of work!!

When 2 secants intersect a circle:
(DC + CE) * CE = (AB + BE) * BE

( 1 + (x+4)) * (x+4) = (11 + (x+1)) * (x+1)

x + x^2 + 4x + 4 +4x +16 = 11x +x^2 +x +11 +x +1

9x + 20 = 13x + 12

4x = 8

x = 2

Source:
http://www.1728.org/circangl.htm
Scroll down to Two Intersecting Secants

Gee - that was a little bit of work!!