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What is the Measure of an Acute Angle?

Instructor: Mark Boster
The world is made up of angles of all kinds; they are all around us and we see them everyday. In this lesson, we will look specifically at acute angles. We will learn how to identify them and measure them.

What is an Acute Angle?

Would you like a piece of pizza? Or maybe a piece of pie? Other than being foods that we like to eat, both of these have something in common - they both have acute angles. The word acute means sharp or pointed. Look at the picture. See how the acute angle is pointy and sharp.

In mathematical terms, an acute angle is one that measures less than 90°, or less than a right angle. So, that would include any angle from 0° up to 89°, and includes both our piece of pie and piece of pizza.

An acute angle measures less than 90 degrees. A right angle measures exactly 90 degrees
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Measuring Angles

Sometimes it is hard to tell the size just by looking at the angle, so you have to measure it. To measure an angle, we use a tool called a protractor. When you line up the bottom line of the protractor on one of the angle lines and put the hole that is in the center bottom of the protractor on the corner of the angle, you can find the measure of the angle. Any measure less than 90° is an acute angle.

A Protractor Measuring 90 degrees
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The Same But Different

How can something be the same but different? Well, think about your father, your mother, yourself and any siblings - you all belong to the same family (maybe you share a last name, like Smith). But all of you do not look the same. Just like your family, acute angles belong to the same family; a family that can be described as any angle between 0° and 89°. But, just like your family, all acute angles do not look the same. Some angles are smaller and some angles are larger, but as long as the angle is less than 90 °, it is acute.

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