Triangles and Related Terms

Triangle

Side

Angle

Vertex

Exterior angle

Opposite interior angle

Opposite side

Altitude

Height

Median

Right

Acute

Obtuse

Equiangular

Equilateral

Isosceles

Scalene

Some Facts about Triangles

A right triangle has only one right angle. Why?

An acute triangle has no right angles or no obtuse angles. Why?

An obtuse triangle has only one obtuse angle. Why?

A triangle is a closed figure whose sides are formed by three segments. Explain.

Complete each statement with always, sometimes, or never.

1. The interior angles of a triangle ___________ add to 180º.
2. A scalene triangle is ________________ an isosceles triangle.
3. An isosceles triangle is _______________ an equilateral triangle.
4. An equilateral triangle is _______________ an isosceles triangle.
5. A unique plane is ______________ formed with three points.
6. Two points ________________ determine exactly one line.
7. The intersection of two lines is ________________ one point.
8. The angle between the hands on a clock is __________________ based on a 1:12 movement of the hands.
9. An acute angle is _________________ greater than 0º and less than 90º.
10. An obtuse angle is _________________ greater than 180º.