Because AE divides ∠DAB equally.

So ∠ DAE = ∠ Mae = ∠ DAB/2

Because AE = AE

so△DAE?△MAE(SAS)

So ∠ DEA = ∠ MEA, MA = DA.

Because it's a split taxi.

So ∠ Abe = ∠ CBE = ∠ cab/2.

Because DA//CB

So ∠ DAB+∠ cab = 180.

So Abe +∠ EAB = 90.

So ∠ bea = 90

So ∠ Meyer +∠ MEB = 90, ∠ DEA+CEB = 90.

So ∠ MEB = ∠ CEB

And because be = be.

So △ BCE △ BME (ASA)

So MB = CB

So ab = MB+ma

That is, ad+BC = ab.