Math Geometry
posted by Tracy on .
A triangle has vertices P(a,b), Q(c,d), and R(e,f). You are asked to prove that the image triangle angle P'Q'R' of triangle angle PQR after reflection across the yaxis is congruent to the preimage. What coordinates should you use for the vertices of triangle measurements P'Q'R?
Sorry, it's long! I'm confuse by this question... Please help!

The vertices of triangle DEF are D (5,3), E (4,3), and F (4,8).
What is the area, in square units, of triangle DEF?