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.