Geometry Unit 3 Vocab

Acute triangle

A triangle in which all three interior angles measure less than 90°.

Equiangular triangle

A triangle with three congruent interior angles (each measuring exactly 60°).

Equilateral triangle

A triangle with three sides of equal length.

Isosceles triangle

A triangle with at least two sides of equal length.

Obtuse triangle

A triangle containing one interior angle that measures greater than 90°.

Right triangle

A triangle containing one interior angle that measures exactly 90°.

Scalene triangle

A triangle where all three sides have different lengths.

Pythagorean theorem

A fundamental geometric principle stating that in a right triangle, the square of the hypotenuse is equal to the sum of the squares of the legs (a²+b²=c²).

Transversal

A line that intersects two or more coplanar lines at distinct points.

Alternate interior angles

Pairs of non-adjacent interior angles that lie on opposite sides of a transversal line.

Alternate exterior angles

Pairs of non-adjacent exterior angles that lie on opposite sides of a transversal line.

Corresponding angles

Pairs of angles that occupy the same relative position at each intersection where a transversal crosses two lines.

Same-side interior angles

Pairs of interior angles that lie on the same side of a transversal line (also called consecutive interior angles).

Interior angle

An angle formed on the inside of a polygon by two adjacent sides.

Exterior angle

An angle formed on the outside of a polygon by one side and the extension of an adjacent side.

Vertex angle of an isosceles triangle

The angle formed by the two congruent sides (legs) of an isosceles triangle.

Base angles of an isosceles triangle

The two angles adjacent to the base, opposite the congruent vertex angle.

Altitude

A perpendicular segment dropped from a vertex of a triangle to the line containing the opposite side.

Centroid

The point of concurrency where the three medians of a triangle intersect (the center of mass).

Circumcenter

The point of concurrency where the three perpendicular bisectors of a triangle's sides intersect.

Concurrent

Three or more lines, rays, or segments that intersect at a single, common point.

Incenter

The point of concurrency where the three angle bisectors of a triangle intersect.

Median

A line segment connecting a triangle's vertex to the midpoint of the opposite side.

Midsegment

A line segment connecting the midpoints of two sides of a triangle.

Orthocenter

The point of concurrency where the three altitudes of a triangle intersect.

Circumscribed circle

A circle that passes through every vertex of a polygon (also called a circumcircle).

Circumscribed polygon

A polygon whose sides are all tangent to a circle enclosed within it.

Inscribed circle

A circle drawn inside a polygon that is tangent to every one of the polygon's sides (also called an incircle).

Inscribed polygon

A polygon whose vertices all lie on the circumference of a surrounding circle.