# Using the protractor

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## How to measure an angle using the protractor

Note the sequence:

• The center O The protractor should be placed over the vertex of the angle.
• The horizontal line through the center must coincide with one of the right angles .
• We check the measure of the scale in which passes the other semi-straight .

## How to build an angle using the protractor

Observe the sequence used to construct an angle of 50º:

• We draw a semi-straight .

• We place the center of the protractor over the origin of the straight (A).

• We identified on the protractor the point (C) corresponding to the 50º measurement.

• Let us draw the straight , obtaining the angle BÂC that measures 50º.

The angles of 30º, 45º, 60º and 90º are special angles. They can be drawn with square.