Understanding Triangle Geometry

Cheat Sheet for 9th Grade Geometry

CircumcenterIntersection of lines bisecting the sides
IncenterIntersection of lines bisecting the angles
AltitudePerpendicular line from a vertex (angle) to the opposite side
OthocenterWhere the altitudes intersect
MedianLine from an angle to the midpoint of the opposite side
CentroidIntersection of the median lines or (x1+x2+x3)/3 , (y1+y2+y3)/3
Distancesqrt((x2-x1)2 + (y2-y1)2)
Pythagarosh = sqrt(a2 + b2)
Liney = mx + b
Midpoint of a line(x1+x2)/2 , (y1+y2)/2
Slope(y2-y1)/(x2-x1) memory aid "rise over run"
Areabase/2 * height

(50,50) A (350,50) C (300,250) B Median lines intersect at the centroid. AB ~= 320.156, AC = 250, BC ~= 206.155