An angle with measure 90° is called a right angle. We shall talk about right angles quite frequently. On a diagram, we use a small square to mean indicate that we have a right angle
Angles smaller than 90 degrees are acute angles and those greater than 90° and less than 180° are obtuse angles. If you click on the "Go" button in the applet you will see examples of acute angles and obtuse angles.
Let us check if you understood the definition. In the applet below you are given the measure of an angle. Decide if it is an acute or obtuse angle and click on the corresponding button.
Adding Angles
When we talk about the sum of two angles A and B we mean a new angle whose measure is the sum of the measures of A and B. When the sum of two angles is 90 ° we call them complementary angles and when the sum is 180° we call them supplementary angles. So, for example 60° is the measure of the complementary angle to 30° while 150° is the measure of the supplementary angle to 30°. You can see examples of supplementary and complementary angles in the applets below.
