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Geometry Chapter 1

acute angle

an angle with a measure greater than 0 degrees and less than 90 degrees


two rays with a common endpoint

angle bisector

A ray that divides an angle into two congruent angles.


the number of square units needed to cover a flat surface


distance around a circle

collinear points

Points that lie on the same line.

complementary angles

Two angles whose measures have the sum of 90 degrees

congruent angles

Angles that have the same measure.

congruent segments

Segments that have the same length


The number that corresponds to a point


figures in the same plane


a series of points that extends in two opposite directions without end


a point that divides a segment into two congruent segments

obtuse angle

An angle that measures more than 90 degrees but less than 180 degrees

opposite rays

two collinear rays with the same endpoint

parallel lines

lines in the same plane that never intersect

parallel planes

planes that do not intersect.


The sum of the lengths of the sides of a polygon.

perpendicular bisector

a segment, ray, line, or plane that is perpendicular to a segment at its midpoint

perpendicular lines

Two lines that intersect to form right angles


A flat surface that goes on forever in all directions


part of a line with one endpoint

right angle

an angle that measures 90 degrees


part of a line with two endpoints

skew lines

lines that do not lie in the same plane

straight angle

an angle whose measure is 180 degrees

supplementary angles

two angles that add up to 180 degrees

vertical angles

two angles whose sides form two pairs of opposite rays

Midpoint Formula

M = [ ( x₂ + x₁) / 2, (y₂ + y₁) / 2 ]
To get your x-coordinate: Add the x's and divide by 2
To get your y-coordinate: Add the y's and divide by 2

Distance formula

d = √[( x₂ - x₁)² + (y₂ - y₁)²]

It does not matter which point is labeled 1 and which is labeled 2

Perimeter of a Rectangle

P = 2L+2W
where L = length and W = width

Perimeter of a Square

P = 4s
where s = length of side

Circumference of a Circle

C=2πr or C=πd
where r = radius and d = diameter and π = pi (approx. 3.14)

Area of a Square

A = s²
where s = length of side

Area of a Rectangle

A = L x W
where L=length and W = width

Area of Circle

where r = radius and π = pi (approx. 3.14)

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