Triangles, Quadrilaterals, and Parts of a Circle

A scalene triangle has no congruent sides. An isosceles triangle has at least two congruent sides. An equilateral triangle has three congruent sides

An acute triangle has only acute angles (less than 90°).
An obtuse triangle has exactly one obtuse angle (more than 90°).
A right triangle has one right angle (equal to 90°)

A quadrilateral is a plane figure with four sides and four angles. We can classify quadrilaterals by the characteristics of their sides and angles

In a parallelogram, opposite sides are parallel and congruent and opposite angles are congruent. A rhombus is a parallelogram with four congruent sides

A rectangle is a parallelogram with four right angles. A square is a rectangle with four congruent sides

A trapezoid is a quadrilateral with exactly two parallel sides

A circle is the set of all points in a plane that are at the same distance from a given point, called the center of a circle. A circle is named by its center

Radius (plural radii) is a line segment whose endpoints are the center of a circle and any point on the circle respectively

Diameter is a line segment that passes through the center of a circle and whose endpoints lie on the circle

Chord is a line segment whose endpoints are any two points on a circle

An arc is a part of a circle named by its end points