We want to reflect our figure over the line g, y = x.
In order to find the vertices of the new figure we just need to exchange the variables
A (x, y) → A' (y, x)
A (7, -5) → A' (-5, 7)
B (x, y) → B' (y, x)
B (7, 3) → B' (3, 7)
C (x, y) → C' (y, x)
C (-2, -7) → C' (-7, -2)
