Geometry Dictionary: Angles

Study Notes

An acute angle is less than 90 degrees but more than 0 degrees
A right angle measures exactly 90 degrees
An obtuse angle is more than 90 degrees but less than 180 degrees
A straight angle measures exactly 180 degrees
Vertical angles are congruent and across from each other when two lines intersect
Adjacent angles share a common ray and vertex, and are next to each other
Complementary angles have a sum of 90 degrees
Supplementary angles have a sum of 180 degrees

Parallel lines never intersect
A transversal is a line that intersects two or more lines
Corresponding angles are in the same position on two parallel lines in relation to a transversal
Alternate interior angles are inside the parallel lines and on opposite sides of the transversal
Alternate exterior angles are outside the parallel lines and on opposite sides of the transversal
Consecutive interior angles are inside the parallel lines and on the same side of the transversal, and their sum is 180 degrees

A triangle is a three-sided figure with a sum of three angles equal to 180 degrees
An equilateral triangle has three congruent sides and three congruent angles
An isosceles triangle has two congruent sides and two congruent angles
A scalene triangle has no congruent sides or angles
A right triangle contains a 90-degree angle
The legs of a right triangle are the two sides that form the 90-degree angle
The hypotenuse of a right triangle is the side opposite the right angle
The Pythagorean theorem is a formula used to find sides of a right triangle

A quadrilateral is a four-sided figure with angles that sum to 360 degrees
A parallelogram is a quadrilateral with opposite sides that are parallel and congruent
A rhombus is a parallelogram with all four sides congruent
A rectangle is a parallelogram with four right angles
A square is a parallelogram with four congruent sides and four right angles
A trapezoid is a quadrilateral with exactly one pair of parallel sides
An isosceles trapezoid is a trapezoid with one pair of congruent sides

A polygon is a closed figure formed by three or more line segments called sides
The sum of interior angles of a polygon can be determined by the number of triangles that can be drawn within the polygon
Congruent polygons have the same size and shape
A congruency statement must match all corresponding angles and sides