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.