Sum of Interior Angles

all inside angles added up

measure of an interior angle of a regular polygon

"the sum of all angles divided by the number of angles"

regular polygon

a polygon with equivalent sides and angles

formula for "Sum of interior angles"

(n - 2)180

sum of exterior angles

all outside angles added up

formula for the sum of exterior angles

always 360

measure of an exterior angle of a regular polygon

"the sum of all angles divided by the number of angles"

formula for an exterior angle of a regulary polygon

360/n

point of concurrency

where three lines meet/intersect

"regular" polygon

equal sides and equal angles

Centroid of a triangle

point of concurrency of the medians; always inside the triangle

median

cuts a line segment in half

Incenter of a triangle

point of concurrency of the angle bisectors; always inside the triangle

angle bisector

cuts an angle in half

Circumcenter of a triangle

point of concurrency of perpendicular bisector; can be inside or outside of the triangle

perpendicular bisector

A line that is perpendicular to a segment at its midpoint.

Orthocenter of a triangle

point of concurrency of the altitudes; can be inside or outside of the triangle

altitude

goes from the vertex to the opposite side, forming a 90 degree angle

vertical angles

a pair of opposite congruent angles formed by intersecting lines

complementary angles

Two angles whose sum is 90 degrees

supplementary angles

Two angles whose sum is 180 degrees

distance formula

d = √[( x₂ - x₁) + (y₂ - y₁)]

midpoint formula

M = [ (x₁ + x₂) / 2, (y₁ + y₂) / 2 ]

perpendicular lines

lines that form a 90 angle; their slopes are opposite reciprocals.

Ex: if the slope of a line is 1/2, the slope of the perpendicular line is -2.

Ex: if the slope of a line is 1/2, the slope of the perpendicular line is -2.

parallel lines

lines that have the same slope, so they never intersect

perimeter

the some of all sides

area

the number of square units needed to cover a flat surface