Ch. 4

right triangle

A right triangle or right-angled triangle is a triangle in which one angle is a right angle. The relation between the sides and angles of a right triangle is the basis for trigonometry. The side opposite the right angle is called the hypotenuse.

scalene triangle

A scalene triangle is a triangle that has three unequal sides, such as those illustrated above. SEE ALSO: Acute Triangle, Equilateral Triangle, Isosceles Triangle, Obtuse Triangle, Triangle

triangle

A triangle is a polygon with three edges and three vertices. It is one of the basic shapes in geometry. A triangle with vertices A, B, and C is denoted.

acute triangle

An acute triangle is a triangle with all three angles acute (less than 90°). An obtuse triangle is one with one obtuse angle (greater than 90°) and two acute angles. Since a triangle's angles must sum to 180°, no triangle can have more than one obtuse angle.

included side and angle

An included angle is the angle between two sides of a triangle. It can be any angle of the triangle, depending on its purpose. The included angle is used in proofs of geometric theorems dealing with congruent triangles. Congruent triangles are two triangles whose sides and angles are equal to each other.

obtuse triangle

An obtuse triangle is a triangle in which one of the angles is an obtuse angle. (Obviously, only a single angle in a triangle can be obtuse or it wouldn't be a triangle.) A triangle must be either obtuse, acute, or right.

corresponding sides

Corresponding sides and angles are a pair of matching angles or sides that are in the same spot in two different shapes. Look at the pictures below to see what corresponding sides and angles look like. Note: These shapes must either be similar or congruent.

adjacent sides

Two lines that meet at a polygon vertex. Usually found in triangles and other polygons , two of the sides that meet at a vertex of the polygon are called adjacent sides.

opposite side and angle

To find a (the length of the side opposite angle A), we can use the tangent function because we know that and we know the length of the adjacent side.

interior angle

the angle between adjacent sides of a rectilinear figure.

corresponding angles

the angles that occupy the same relative position at each intersection where a straight line crosses two others. If the two lines are parallel, the corresponding angles are equal.

vertex

the highest point

quadrangular triangle

triangle with 4 sides

cpoctac

two triangles are congruent

base of an isosceles triangle

In an isosceles triangle that has exactly two equal sides, the equal sides are called legs and the third side is called the base. The angle included by the legs is called the vertex angle and the angles that have the base as one of their sides are called the base angles.

vertex angle of an isosceles triangle

In an isosceles triangle that has exactly two equal sides, the equal sides are called legs and the third side is called the base. The angle included by the legs is called the vertex angle and the angles that have the base as one of their sides are called the base angles. The vertex opposite the base is called the apex.

isosceles triangle

In geometry, an isosceles triangle is a triangle that has two sides of equal length. Sometimes it is specified as having two and only two sides of equal length,

base angle of an isosceles triangle

In isosceles triangle RST, angle S is the vertex angle. Base angles R and T both measure 64 degrees.

legs of an isosceles triangle

Special Names for Sides and Angles. Legs, base, vertex angle, and base angles. In an isosceles triangle, the two equal sides are called legs, and the third side is called the base. The angle formed by the two equal sides is called the vertex angle.

sides of a triangle

The hypotenuse of a right triangle is always the side opposite the right angle. It is the longest side in a right triangle. The other two sides are called the opposite and adjacent sides. These sides are labeled in relation to an angle.

congruent figures

Two polygons are congruent if they are the same size and shape - that is, if their corresponding angles and sides are equal. Move your mouse cursor over the parts of each figure on the left to see the corresponding parts of the congruent figure on the right.

corollary

forming a proposition that follows from one already proved.

equilateral triangle

in geometry, an equilateral triangle is a triangle in which all three sides are equal. In the familiar Euclidean geometry, equilateral triangles are also equiangular;

exterior angle

the angle between a side of a rectilinear figure and an adjacent side extended outward.