Section 3.3 Polygons

A polygon is a figure in a plane formed by fitting line segments together end-to-end in such a way as to form a closed figure.

The sum of the measures of the angles of any triangle is equal to 180^o.

An equilateral triangle is a triangles with three equal sides (and three equal angles).

An isosceles triangle is a triangle that has two equal sides.

A scalene triangle is a triangle that has sides with three different lengths.

An obtuse triangle is a triangle that has an obtuse angle as one of its angles, i.e., an angle greater than 90^o.

An acute triangle is a triangle that has acute angles for all of its angles, i.e., all angles are less than 90^o.

A right triangle is a triangle containing a right angle, i.e., an angle equal to 90^o.

The hypotenuse of a right triangle is the side opposite of the right angles and is the longest side of the triangle. The other sides are called legs.

A quadrilateral is a polygon with four sides.

A parallelogram is a quadrilateral that has both pairs of opposite sides parallel and of equal length. Both pairs of opposite angles are equal in measure.

A rhombus is a parallelogram with all sides equal in length. Thus both pairs of opposite sides are parallel and both pairs of opposite angles are equal in measure.

A rectangle is a parallelogram containing a right angle. Both pairs of opposite sides are equal in length, and both pairs of opposite angles are equal in measure.

A square is a rectangle with all four sides equal in length.

A trapezoid is a quadrilateral that has exactly one pair of parallel sides.