Review: An angle is two rays with a common endpoint, called the vertex.  You can classify angles according to their size: acute, obtuse, or right. 

Let's start with the right angle, because it is part of the definitions of the other two.  A right angle's two rays meet at a 90° angle.  They are perpendicular to each other.

Think of the angle that is made where the floor meets the wall, or the wall meets the ceiling in your classroom.

Less than 90 ° angles are called acute angles.  The distance between the two rays is smaller that 90°.  These angles will fit INSIDE a right angle.  

Here are some other examples of acute angles. 

Greater than 90° angles are called obtuse angles.  They are larger than right angles.  Obtuse angles measure between 91° and 179°. 

A right angle fits inside an obtuse angle, with some left over!

An angle can only be classified as ONE of the above, e.g. an angle cannot be both acute and obtuse, or right and acute. 

borders courtesy of bellsnwhistles.com

Let's Practice!