You already know they are the same, you just have to have proof.
To calculate slope of a line, take two points on that line and use this equation:
Plug the first set of points, (4, 5) in for y1 and x1, and plug (1, 2) in for y2 and x2. Use the equation to find that the slope of the equation is slope = 1.
Do the same for the bottom triangle and you will see that slope = -1