Geometry Terms and Definitions

Front

acute angle

Back

An angle that is smaller than a right angle; its measure is less than 90°.

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acute triangle

Back

A triangle that contains all acute angles.

Front

adjacent angles

Back

Two angles with the same vertex that share a ray and do not overlap.

Front

angle

Back

A figure formed by two rays with the same endpoint.

Front

complementary angles

Back

Two angles are complementary if the sum of their measures is 90°.

Front

degree

Back

The unit used to measure angles. An angle that turns through of a circle is a one-degree (1°) angle.

Front

equilateral triangle

Back

A triangle with all sides of equal length.

Front

figure

Back

A set of points in a flat space. Sometimes refers to common shapes like triangles, rectangles, trapezoids, etc.

Front

intersect

Back

Two or more lines (or line segments or rays) meet or cross at a point.

Front

isosceles triangle

Back

A triangle with at least two sides of equal length. An equilateral triangle is also an isosceles triangle.