How can we help?

You can also find more resources in our Help Center.

Square

4 equal sides. 90 degree angles.

Rectangle

quadrilateral. 90 degree angles.

Quadrilateral

4-sided polygon

Perimeter

distance around a figure

Area

number of square units it takes to cover a figure

Base

bottom of a figure

Height

the line that makes a 90 degree angle with the base

Right Angle

90 degree angle

Triangle

3-sided polygon

Acute Triangle

3-sided polygon, 1 angle greater than 90 degrees

Obtuse triangle

...

Right Triangle

3-sided polygon. One 90 degree angle.

Isosceles Triangle

3-sided polygon. 2 congruent sides.

Equilateral Triangle

3-sided polygon. 3 congruent sides. 3 60 degree angles.

Scalene Triangle

3-sided polygon. No congruent sides

Leg

the 2 sides that make the right angle in a right triangle

hypotenuse

side opposite the right angle in a right triangle

parallelogram

4-sided quadrilateral. 2 pairs of parallel lines

parallel lines

lines that will never intersect

trapezoid

4-sided quadrilateral. 1 pair of parallel lines

congruent

same size, same shape

rhombus

4 equal-sided polygon

segment

line between two points

vertex or vericies

the point where 2 lines meet

polygon

many-sided figure, closed, straight line segment

regular polygon

polygon with congruent sides and congruent angles

irregular polygon

polygon without all congruent sides

straight angle

angle measuring 180 degrees

circle

infinite set of points equidistant from a centerpoint

radius

half the diameter

diameter

distance across a circle through the center point

pi

ratio of circumference of a circle to its diameter, irrational; = 3.14

circumference

distance around a circle

semi-circle

half of a circle

complementary angles

angles whose sum equals 90 degrees

Supplementary angles

angles whose sum equals 180 degrees

interior angle

angles inside of a polygon

exterior angle

angle made when you extend one of the sides of the polygon outside from the polygon

pentagon

5-sided polygon

hexagon

6-sided polygon

heptagon

7-sided polygon

octagon

8-sided polygon

nonagon

9-sided polygon