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.