point
single spot, no dimensions (small), one uppercase letter
segment
line with two end points, finite # points, 1D
line
goes forever both directions, infinite # points, 1D
ray
1 defined end, infinite # points, 1D
plane
labeled 3 or more letters, non collinear, 2D
midpoint formula
(x₁+x₂)/2, (y₁+y₂)/2
distance formula
square root of (x2-x1)^2 + (y2-y1)^2
dissect
point cuts in half, only to a segment not a line
skew
not parallel, not intersecting, different directions (dimensions)
acute angle
more than 0, less than 90 degrees
obtuse angle
more than 90, less than 180 degrees
right angle
90 degrees
straight angle
180 degrees
adjacent angles
form a right angle, add to 90
supplementary angles
form a straight angle, add to 180
linear pair
two adjacent angles, form a straight line
vertical angles
share a vertex, across from each other, congruent
angle bisector
ray or line, cutting angle in half