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Lesson · Grade 6 · Mathematics

Measuring and Drawing Angles with a Protractor

  • Grade 6
  • Mathematics
  • 1 min 37 s
  • British Columbia
  • BC6-MA-34

A 130° angle is first estimated with angles we already know (more than 90°, less than 180°, about 90° + 45° = 135°), then measured by putting the protractor's centre on the vertex, lining the zero line up with one arm, and counting up from that arm's 0 to 130°, with the other scale's 50° ruled out by the estimate and 130° named as obtuse. The same angle is then drawn from an arm pointing the other way, counting up from the other scale's 0 to mark a dot, joining it to the vertex and checking it is more than 90°, before a one-line recap of the steps.

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In one sentence

The question this lesson answers

How big is this angle, in degrees?

First, estimate, using angles we know: 45, 90 and 180 degrees.

Transcript

What the lesson says

How big is this angle, in degrees?

First, estimate, using angles we know: 45, 90 and 180 degrees.

Our angle is more than 90 degrees, but less than 180 degrees.

It is about 90 plus 45, so we estimate 135 degrees.

Put the centre of the protractor on the vertex, where the arms meet.

Turn it so the zero line lies along one arm.

Start at 0 on that arm, and count up to the other arm: 130 degrees.

The other scale says 50, but we estimated about 135, so it is 130 degrees.

An angle between 90 and 180 degrees is called obtuse.

Now let us draw an angle of 130 degrees.

Draw one straight arm, and mark the vertex at one end.

Put the centre on the vertex, and the zero line along the arm.

Count up from the 0 on this arm to 130, and make a dot.

Take the protractor away, and join the dot to the vertex.

Check: it is more than 90 degrees, just as a 130 degree angle should be.

Estimate first, then put the centre on the vertex, the zero line on one arm, and count up from 0.

Curriculum

Where this fits

British Columbia, Grade 6

Mathematics, Geometry and measurement: angle measurement and classificationBC6-MA-34

Previous: Five Types of Angles: Acute, Right, Obtuse, Straight and ReflexNext: How Much Does a Box Hold? Cubic Centimetres, Millilitres and Litres

The outcomes and strands follow the British Columbia curriculum.

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