Basic Geometry Vocabulary

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Angle

Back

An angle is formed by two rays that share a common endpoint. The rays are called the sides of the angle, and the common endpoint is called the vertex.

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Acute Angle

Back

An acute angle is an angle that measures less than 90°. Think of it as a small, sharp angle.

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Obtuse Angle

Back

An obtuse angle is an angle that measures greater than 90° but less than 180°. It's a wide, open angle.

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Right Angle

Back

A right angle is an angle that measures exactly 90°. It often looks like the corner of a square.

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Complementary Angles

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Complementary angles are two angles whose measures add up to 90°. They "complement" each other to form a right angle.

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Supplementary Angles

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Supplementary angles are two angles whose measures add up to 180°. They "supplement" each other to form a straight line.

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Vertical Angles

Back

Vertical angles are two non-adjacent angles formed by two intersecting lines. They are always equal in measure (congruent). Think of them as angles "across" from each other.

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Linear Pair

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A linear pair is a pair of adjacent angles that form a straight line. Their measures always add up to 180° (they are supplementary).

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Angle Bisector

Back

An angle bisector is a line or ray that divides an angle into two equal parts.

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Parallel Lines

Back

Lines in the same plane that never intersect, maintaining the same distance apart.