ANSWER
The coordinates of the third vertices are
or
.
EXPLANATION
Let the hypotenuse of the right angle triangle have vertices
and
.
The third point is the intersection of the horizontal line that passes through (6,-2), that has equation
and the vertical line that passes through
which also has equation
.
Hence one possible coordinates of the third vertex is
.
The third vertex could also be the intersection of the vertical line that passes through (6,-2), that has equation
and the horizontal line that passes through
which also has equation
.
Hence another possible coordinates of the third vertex is
.
See diagram in attachment