Angles are measured in degrees. A circle (a complete rotation) is 360 degrees.
© July 2003 Rasmus ehf.
Geometry - Angles and degrees
Lesson 1.
Angles are measured in degrees. A
circle (a complete rotation) is 360 degrees.
Look at 1/4 of a circle.
Some common angles
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A 90° angle is called a right angle. |
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An angle between 90° and 180° is called an obtuse angle. |
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An angle that is less than 90° is called an acute angle. |
More about angles, degrees and similar figures
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Half a circle is 180 degrees (a straight angle). |
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Supplementary angles are angles that have an arm in common and have a sum of 180 degrees. The green and blue angles have a sum of 180 degrees. |
Example:
How many degrees is angle X?
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Calculate: |
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Similar figures
Figures with exactly the same shape are similar figures. Corresponding angles in similar triangles are equal in size. This rule applies to all polygons.
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Similar figures |
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Similar figures |
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Similar figures |
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not similar |
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not similar |
Sums of angles
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In a triangle, the angles add up to 180°. |
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In a rectangle, the angles add up to 360°. |
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In any quadrilateral, the angles add up to 360°. This diagram shows a parallelogram |
Practice these methods and try Quiz 1 on Geometry. Remember to use the Checklist to keep track of your work.
