Do you find geometry terms confusing? Take a look at this study guide, which includes the most important geometry terms you’ll need to know.

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### Types of Angles

Angles are one of the most basic concepts in geometry, and there are many geometry terms that refer to them.

*Acute*angles are less than 90 degrees,*obtuse*angles are more than 90 degrees, and*right*angles are exactly 90 degrees. If two angles are*complementary,*they add up to 90 degrees, and if two angles are*supplementary,*they add up to 180 degrees. - slide 2 of 6
### Types of Triangles

Triangles are defined by the types of angles that make them up. A

*right*triangle has one right angle and two acute angles. An*isosceles*triangle has two equal angles (and two equal sides as well). An*equilateral*triangle has three equal angles (and three equal sides as well). - slide 3 of 6
### Types of Lines

There are two main geometry terms referring to types of lines that are important to know: parallel and perpendicular.

*Parallel*lines are lines that will never meet, no matter how far they are extended both ways (like the opposite sides of a square).*Perpendicular*lines are lines that meet at a 90 degree angle (like adjacent sides of a square). - slide 4 of 6
### Types of Shapes

The study of geometry is often thought of as the study of shapes. Everyone knows the definition of

*triangle*,*circle*, and*square*, but what about*polygon*,*octagon*, and*pentagon*? Just break apart the word into prefixes and roots to find that*polygon*is a shape with many sides,*octagon*is a shape with eight sides, and*pentagon*is a shape with five sides. - slide 5 of 6
### Types of Measurements

Some of the most basic geometry terms have to do with measuring parts of a shape. The

*perimeter*of a shape is the distance around the lines that make it up. The*area*of a shape is the measurement of the space inside of it. The*circumference*of a shape is essentially the perimeter, but it can only refer to the “perimeter" of a circle. - slide 6 of 6
### Circle Terms

In addition to circumference and area, there are three other main terms that apply solely to circles. The vertex of a circle is the point in the direct center of the circle. The

*radius*of a circle is the distance from the vertex to any point on the circle. The*diameter*of a circle is the distance from one point on the circle to another, passing through the vertex. The diameter of a circle cuts a circle in half, and it is always twice the length of the radius.