So ACB angle = BEC angle =90 degrees,

So angle ACE+ angle BCE=90 degrees, angle B+ angle BCE=90 degrees,

So angle ACE= angle b,

Because FD//BC,

So angle ADF= angle b,

So angle ACE= angle ADF,

Because AF bisects the angle CAB,

So angle CAF= angle DAF,

And AF=AF,

So triangle ACF is equal to triangle ADF(A, a, s),

So AC=AD.