# Angle types review

CCSS Math: 4.G.A.1
Review the following types of angles: acute, right, obtuse, and straight.  Identify and draw types of angles in some practice problems.

### Summary of angle sizes

Angle typeAngle size (in degrees)
AcuteBetween $0^\circ$ and $90^\circ$
RightExactly $90^\circ$
ObtuseBetween $90^\circ$ and $180^\circ$
StraightExactly $180^\circ$

### Right angles

A right angle is a $90^\circ$ angle. A right angle is in the shape of a perfect corner, like the corner of a rectangular sheet of paper. Below is an example of a right angle.

### Straight angles

A straight angle is a $180^\circ$ angle. A straight angle looks like a straight line. Below is an example of a straight angle.

### Acute angles

An acute angle is an angle whose degree measure is less than $90^\circ$. Below is an example of an acute angle.
When we compare an acute angle to a $\blueD{\text{right angle}}$, we can see that an acute angle is less than $90^\circ$.

### Obtuse angles

An obtuse angle is an angle whose degree measure is greater than $90^\circ$ but less than $180^\circ$. Below is an example of an obtuse angle.
When we compare an obtuse angle to a $\blueD{\text{right angle}}$, we can see that an obtuse angle is greater than $90^\circ$.
When we compare an obtuse angle to a $\greenD{\text{straight angle}}$, we can see that an obtuse angle is less than $180^\circ$.