Quadrilaterals and Pythagoras Theorem

Hi, new to this,

The diagonals AC and BD, of a quadrilateral ABCD, are perpendicular. Find the length of AB, if BC=5cm, DC=4cm and AD=3cm. Let the intersection of the diagonals be E.

Now I'm thinking the answer will be in surd form. I've been thinking about the question for a while but i don't really know how to go about answering it.

Thanks in advance.:)

Thanks, want to clear something up.

Thanks for the help,

So is

because that essentially is the same as

The two 's and 's cancel out, equalling

Thanks:)