Three Types of Angles

On this web page you can explore three types of angles—right, acute, and obtuse. This will help you write definitions and begin to visually recognize the three types of angles.


Drag the red points that define angle ABC. Notice that the word in the angle changes according to the measure of the angle.

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  1. Drag the points to make angle ABC a right angle. What is the angle measure for the right angle? Write a definition for right angle.
  2. What are the angle measures for acute angles? What angle measures are not acute angles? Write a definition for acute angle.
  3. Use the sketch to find examples and counterexamples of obtuse angles. Write a definition for obtuse angle.
  4. There are two measures that are not labeled right, acute, or obtuse. What measures are they? Why do you think these measures are not classified?
  5. Press Show Angles and look at angles DEF, GHI, JKL, MNO, and PQR. Decide whether each is acute, obtuse, or right. Write down your guesses.
  6. Drag the points of angle ABC into position over angle DEF so the two angles match exactly. Note the angle measure and the type of angle. Was your guess in step 5 correct or incorrect?
  7. Repeat step 6 to check your guesses for angles GHI, JKL, MNO, and PQR.