- Angles, Lines, and Polygons
- Home
- Measuring an angle with the protractor
- Acute, obtuse, and right angles
- Naming segments, rays, and lines
- Identifying parallel and perpendicular lines
- Acute, obtuse, and right triangles
- Classifying scalene, isosceles, and equilateral triangles by side lengths or angles
- Finding an angle measure of a triangle given two angles
- Naming polygons
- Drawing and identifying a polygon in the coordinate plane

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We measure angles in degrees. Angles can also be measured in other units like radians. One complete rotation around a point is 360 degrees or 2 pi radians. We use a little circle ° following the number to mean degrees. For example, 60° means 60 degrees. A full circle is 360°; half a circle is 180° and quarter a circle in 90°.

We often measure angles using a protractor. The normal protractor measures 0° to 180°

An **acute angle** is defined as an angle that is more than 0° but less than 90° in measure.

A **right angle** is defined as an angle that is 90° in measure.

An **obtuse angle** is defined as an angle that is between 90° and 180° in measure.

Classify each angle as acute, obtuse, right or straight

**Step 1:**

Given angle is equal to 90°.

**Step 2:**

So, the given angle is a right angle.

Classify each angle as acute, obtuse, right or straight

**Step 1:**

Given angle is equal to 180°.

**Step 2:**

So, the given angle is a straight angle

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