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# Geometry Terms

### Plane Geometry

TermDefinition
Angle Formed by two rays, or sides, with a common endpoint called the vertex.
Acute Angle The measure of the angle is greater than 0° and less than 90°.
Right Angle The measure of the angle is 90°.
Obtuse Angle The measure of the angle is greater than 90° and less than 180°.
Straight Angle The measure of the angle is 180°.
Complementary Angles Two angles whose measures add to 90°.
Supplementary Angles Two angles whose measures add to 180°.
Adjacent Angles Angles with a common vertex and a common side, but no common interior points.
Congruent Angles Angles that have the same measure.
Vertical Angles Nonadjacent angles formed by two intersecting lines.
Parallel Lines Lines in a plane that never meet.
Perpendicular Lines Lines that intersect at 90° angles.
Transversal A line that intersects two or more lines that lie on the same plane.
Triangle Sum Theorem The theorem that says the angle measures of a triangle add to 180°.
Acute Triangle A triangle with 3 acute angles.
Right Angle A triangle with 1 right angle.
Obtuse Triangle A triangle with 1 obtuse angle.
Equilateral Triangle A triangle with 3 congruent sides and 2 congruent angles.
Isosceles Triangle A triangle with at least 2 congruent sides and 2 congruent angles.
Scalene Triangle A triangle with no congruent sides and no congruent angles.
Triangle Inequality Theorem The theorem states that the sum of any 3 sides of a triangle is greater than the 3rd side.
Polygon A closed plane figure formed by 3 or more segments.
Trapezoid A polygon with exactly 1 pair of parallel sides.
Parallelogram A polygon with 2 pairs of parallel sides.
Rectangle A polygon with 4 right angles.
Rhombus A polygon with 4 congruent sides.
Square A polygon with 4 congruent sides and 4 right angles.
Midpoint The point that divides a segment into 2 congruent segments.
Created by: allvasquez