Acute angles are angles of less than ninety degrees.

For example: The angles below are acute angles.

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We use a protractor for measuring angles in degrees. Below is a picture of a protractor and how we use it. Place the centre of the zero line above the angle at A, the zero line should be covering one side of the angle. Starting at zero, follow the scale around to the other side of the angle and read off the number of degrees (41^o in the angle below).

Note: we are using the inside scale because it is the one which starts at zero (The outside scale starts at 180^o).

If we were measuring the angle on the other side, starting from the left, then we would use the outside scale and the result would be 139^o.

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Written Angle Notation
 

Angles are written in the following ways:

1) Using three capital letters, with the angle sign over the middle letter.

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