posted by Tracy .
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 y-axis 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!
Math Geometry -
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?