So angle DEF= angle AEF=90 degrees, and side AE= side de.

Common edge EF

So triangle DEF is congruent with triangle AEF (SAS)

So angle ADF= angle DAF

Because angle ADF= angle B+ angle BAD

Angle DAF= angle CAF+ angle DAC

AD is the bisector angle of angle a BAD= angle DAC.

So angle B= angle CAF

2 AD bisects angle BAC, so angle BAD = angle DAC.

CE is perpendicular to AD, so angle AOE= angle AOC.

So the triangle is congruent with the triangle Cao (Asa).

So EO side OC side

Divide CE vertically in a triangle

So the triangle DCE is an isosceles triangle.

Angle DEC= angle DCE

Because EF and BC are parallel

So angel ·CEF = angel ·DCE

So angle DEC= angle CEF EC divides the angle equally.