Measurement and Types of Angles
Types of angles are grouped by their size in degrees. An acute angle is under 90°, an obtuse angle is 90° to 180°, and a reflex angle is over 180°. You measure them with a protractor.
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What is an Angle?
- An angle is formed when two lines meet at a point, called the vertex.
- Angles are measured in degrees (°).
Types of Angles
- Acute angle: < angle <
- Obtuse angle: < angle <
- Reflex angle: < angle <
How to Measure Angles?
- Place the centre of the protractor on the vertex.
- Align the zero line with one arm and read where the other arm crosses the scale.
Measuring Angles Greater Than
- Measure the smaller angle first using the protractor.
- Subtract from to find the reflex angle.
How to Draw Angles?
- Draw a straight line for one arm of the angle.
- Place the protractor, mark the required angle, then draw the second arm.
Drawing Angles Greater Than
- Subtract the given angle from to find the smaller angle.
- Draw the smaller angle, and the reflex angle is the one you need.
Practice Questions
Test your understanding
What is the measure of a straight angle?
Correct! 🎉 +10 pointsNot quite right
A straight angle forms a straight line and always measures .
Which of these is an acute angle?
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An acute angle is greater than and less than . satisfies this.
What is the sum of the angles in a full circle?
Correct! 🎉 +20 pointsNot quite right
A full circle always measures .
Construct a angle using a protractor. What smaller angle should you first draw?
Correct! 🎉 +20 pointsNot quite right
To construct , subtract from a full turn: .
An angle measures . What type of angle is it?
Correct! 🎉 +20 pointsNot quite right
An obtuse angle is greater than but less than .
Two angles form a straight line. One angle is 5 times the size of the other angle. What is the measure of the larger angle?
Correct! 🎉 +30 pointsNot quite right
A straight line is . Dividing into 6 equal parts gives . The larger angle is .
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Students Also Ask
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An acute angle is any angle greater than 0° and less than 90°. It looks sharp and narrow. An acute angle is smaller than a right angle, which measures exactly 90°, so it is the smallest of the named angle types.
An obtuse angle is greater than 90° but less than 180°. It is wider than a right angle yet still smaller than a straight angle. On a protractor, an obtuse angle takes the larger of the two numbers where its arm crosses the scale.
A reflex angle is greater than 180° but less than 360°. It is larger than a straight angle but smaller than a full turn. A protractor cannot measure a reflex angle directly, because a protractor only reaches 180°, so you measure its smaller counterpart instead.
There are six main types of angle, grouped by size. They are the acute angle, the right angle, the obtuse angle, the straight angle, the reflex angle, and the full angle. Each one covers a different range of degrees, from below 90° up to a full turn of 360°.
You use a protractor to measure an angle. You line up the protractor's centre with the vertex and its zero line with one arm, then read where the second arm crosses the scale. For an acute angle you read the smaller number, and for an obtuse angle the larger.
A protractor only measures angles up to 180°, but a reflex angle is greater than 180°. This means the reflex angle falls outside the protractor's scale. Instead, you measure the smaller angle beside it and subtract that from 360° to find the reflex angle.