Cheat Sheet for 9th Grade Geometry
| Circumcenter | Intersection of lines bisecting the sides |
| Incenter | Intersection of lines bisecting the angles |
| Altitude | Perpendicular line from a vertex (angle) to the opposite side |
| Othocenter | Where the altitudes intersect |
| Median | Line from an angle to the midpoint of the opposite side |
| Centroid | Intersection of the median lines or (x1+x2+x3)/3 , (y1+y2+y3)/3 |
| Distance | sqrt((x2-x1)2 + (y2-y1)2) |
| Pythagaros | h = sqrt(a2 + b2) |
| Line | y = mx + b |
| Midpoint of a line | (x1+x2)/2 , (y1+y2)/2 |
| Slope | (y2-y1)/(x2-x1) memory aid "rise over run" |
| Area | base/2 * height |