Measure and draw angles
Objective. Use a protractor accurately and classify angles.
- 1. Learn
- 2. Worked example
- 3. Practice
- 4. Feedback
- 5. Continue
Learn: the key idea
An angle measures the amount of turn between two lines meeting at a point, measured in degrees using a protractor. To measure an angle accurately, place the centre of the protractor exactly on the vertex and align the baseline with one arm of the angle, then read where the other arm crosses the scale. Angles are classified by size: acute angles are less than 90°, right angles are exactly 90°, obtuse angles are between 90° and 180°, and reflex angles are greater than 180°. Drawing an angle follows the reverse process, marking the required degree measurement from the baseline.
Worked example
Classify an angle that measures 112° after being measured with a protractor.
- 1Recall the categories: acute less than 90°, right exactly 90°, obtuse between 90° and 180°, reflex more than 180°.
- 2Compare 112° to 90°: it is greater than 90°.
- 3Compare 112° to 180°: it is less than 180°.
- 4Since it falls between 90° and 180°, classify accordingly.
Answer: Obtuse angle
Concept mastery
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Practice
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Start practisingCommon mistake. Pupils often read the wrong scale on a protractor, reading 150° instead of 30° because they used the outer scale instead of the inner one. Always check which scale starts at 0° on the baseline arm.
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