Why is the specific angular momentum equal to this?

[Bob Jones]

From a wiki's vis-viva equation page, it is given that the specific angular momentum h is also equal to the following:

h = wr^2 = ab * n

How can ab * n be derived to be equal to the angular momentum using elliptical orbit energy/momentum/other equations without having to use calculus or equations involving eccentricity?

 

[Bob Jones]

Oh... Wait. This is the old version of this. I understand how it works now. Could someone tell me how geometrically or algebraically you can derive b² = r_a * r_b?