That means
AC and GE are parallel lines, and also AG and CE are parallel lines.
Whenever 2
lines are perpendicular, they form 90°. If the second line is perpendicular to
the third line, then the third line is rotated 180° with respect to the first line (90°+90°=180°). Rotating a line 180° looks the same as rotating it 360°,
because they are simetric. Rotating a line 360° is the same as not rotating it
at all. The only difference is that it may be above or below, but with the same
slope. When 2 lines have the same slope, they are parallel.
