Solution: because Be is perpendicular to CE? Advertising vertical CE

So angle E= angle BCA=90 degrees.

Because angle BCE is equal to angle BCA- angle ECA=90 degrees-angle ECA.

Angle DAC=90 degrees-Angle ECA?

So angle e is equal to angle BCE.

Because at △BEC and △CDA,

∠E=∠BCE

∠E=∠BCA

BC=AC

So △ BEC △ CDA (AAS)

So CE=DA=2.5CM.

CD=BE

DC = EC-ED = 2.5cm- 1.7cm = 0.8cm

So BE=0.8CM.