Angles with a protractor
Draw BC = 5.5 cm and, with a protractor, construct ∠ABC = 25° at B.
Draw BC = 5.5 cm and, with a protractor, construct ∠ABC = 35° at B.
Draw BC = 5 cm and, with a protractor, construct ∠ABC = 78° at B.
Draw BC = 5 cm and, with a protractor, construct ∠ABC = 115° at B.
Draw BC = 5 cm and, with a protractor, construct ∠ABC = 150° at B.
Draw BC = 5.5 cm and, with a protractor, construct ∠ABC = 47° at B.
1. Draw BC = 5.5 cm with a ruler.
2. Put the center of the protractor on B and its base line exactly on BC.
3. Count from 0° on the side of BC up to 25°, and mark a point A there.
4. Take the protractor away and join BA with the ruler: ∠ABC = 25°.
1. Draw BC = 5.5 cm with a ruler.
2. Put the center of the protractor on B and its base line exactly on BC.
3. Count from 0° on the side of BC up to 35°, and mark a point A there.
4. Take the protractor away and join BA with the ruler: ∠ABC = 35°.
1. Draw BC = 5 cm with a ruler.
2. Put the center of the protractor on B and its base line exactly on BC.
3. Count from 0° on the side of BC up to 78°, and mark a point A there.
4. Take the protractor away and join BA with the ruler: ∠ABC = 78°.
1. Draw BC = 5 cm with a ruler.
2. Put the center of the protractor on B and its base line exactly on BC.
3. Count from 0° on the side of BC up to 115°, and mark a point A there.
4. Take the protractor away and join BA with the ruler: ∠ABC = 115°.
1. Draw BC = 5 cm with a ruler.
2. Put the center of the protractor on B and its base line exactly on BC.
3. Count from 0° on the side of BC up to 150°, and mark a point A there.
4. Take the protractor away and join BA with the ruler: ∠ABC = 150°.
1. Draw BC = 5.5 cm with a ruler.
2. Put the center of the protractor on B and its base line exactly on BC.
3. Count from 0° on the side of BC up to 47°, and mark a point A there.
4. Take the protractor away and join BA with the ruler: ∠ABC = 47°.
Why it works
A protractor is a half circle marked in 180 equal parts, each 1°, from its center. With the center on B and 0° along BC, the mark at the reading is the direction that makes that angle with BC. Count from the 0° that lies on BC: the other row of numbers gives 180° minus the angle.