4. Acute angle
An angle that measures less
than ninety degrees but more
than zero degrees
5. Right angle
An angle of 90°, as in a corner
of a square, or formed by
dividing a circle into quarters.
6. Obtuse angle
An angle that measures more
than 90 degrees but less than
180 degrees
7. Straight angle
Two lines that form a right
angle are said to be normal,
orthogonal, or perpendicular.
Angles larger than a right
angle and smaller than a
straight angle (between 90°
and 180°) are called obtuse
angles ("obtuse" meaning
"blunt").
8. Reflex angle
The reflex angle is the
larger angle. It is more than
180° but less than 360° If you
choose the smaller angle you
might have an Acute Angle, or
an Obtuse Angle instead: The
larger angle is a Reflex Angle,
but the smaller angle is an
Acute Angle.
9. Full angle
A full angle, also called a
perigon, is an angle equal to
radians corresponding to the
central angle of an entire
circle. Four right angles or
two straight angles equal one
full angle
