Astudent solved the following problem and made an error:

triangles abc and def. angles a and f are congruent and measure 135 degrees. coordinates for the vertices are at a 0, 2 and b 2

line 1 segment ac equals 2, segment df equals 2, segment ac is congruent to segment df
line 2 ∠a ≅ ∠f
line 3 length of segment ab.
a (0, 2)
b (2, 4)
d equals square root of quantity x sub 2 minus x sub 1 squared plus quantity y sub 2 minus y sub 1 squared, then d equals squar
segment ab= 2.83
line 4 length of segment fd.
d (2, 0)
f (4, 2)
d equals square root of quantity x sub 2 minus x sub 1 squared plus quantity y sub 2 minus y sub squared then d equals square r
segment fd= 2.83
line 5 segment ac is congruent to segment fd
line 6 triangle abc is congruent to triangle fde by sas

in which line did the student make the first mistake?