we know that
If two triangles are congruent, then its corresponding sides and its corresponding angles are congruent
In this problem
XW=YZ ------> is given
WA=ZA -----> is given
XA=YA -----> by Apply Pythagorean Theorem in a right triangle
and
is given
that means
two corresponding sides and the angle between the two sides are congruent
so
triangle XWA and triangle YZA are congruent by SAS
