Consider the figure.

Find AB if BC = 4, BD = 5, and AD = 5

so I think it's a rectangle. and AB is the diagnal line. to find AB, we need to use the hypothegorin teorin.

BD=5, DA=5

let x represent the AB

formula = a²+b²=c²

= 5²+5² = x²

= 25+25=x²

=50=x²

=square root of 50 = 7.07

AB is 7.07