Is this equivalent to the Pythagorean Theorem?

[Quine!]

So I was reading up on the Pythagoreans, and I came across this page: http://www.math.ufl.edu/~rcrew/texts/pythagoras.html .

I don't see the reasoning behind this statement.

"Since AB=AD+DB, adding these equations yields

A(B²)=A(C²)+C(B²)
which is the Pythagorean theorem."

I tried some simple algebra on this statement and couldn't get Pythag to fall out of it. Can someone figure out a derivation for this?

 

[Muphrid]

That's not what the page says. It says,

$$AB^2 = AC^2 + CB^2$$

A, B, and C are not variables. $AB$ represents the length between points A and B. You should read $AB^2$ as a single length being squared.