###
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.

###
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

### Please allow access to your computer’s microphone to use Voice Recording.

## We can’t access your microphone!

### Click the icon above to update your browser permissions above and try again

Example:

### Reload the page to try again!

Reload

## Press Cmd-0 to reset your zoom

## Press Ctrl-0 to reset your zoom

### It looks like your browser might be zoomed in or out. Your browser needs to be zoomed to a normal size to record audio.

## Your microphone is muted

### For help fixing this issue, see this FAQ.