Mrs. Smith Sums It Up
compass and protractor
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How to use a compass:

Compass

A compass is an instrument used to draw circles or the parts of circles called arcs.  It consists of two movable arms hinged together where one arm has a pointed end and the other arm holds a pencil.

Note that a compass is also called a pair of compasses.


To draw a circle (or arc) with a compass:

  • make sure that the hinge at the top of the compass is tightened so that it does not slip
  • tighten the hold for the pencil so it also does not slip
  • align the pencil lead with the compass's needle
  • press down the needle and turn the knob at the top of the compass to draw a circle (or arc)


Example 2

Use a compass to draw a circle of radius 4 cm.

How to Use a Protractor

link to how to

Using a protractor to measure angles
(For assistance see www.mathopenref.com/constmeasureangle.html)
1.   The figure below is an irregular triangle.
  (a) Measure the 3 internal angles with a protractor and add them up.
  (b) Can you draw a circle inside the triangle with your compass so that the circle touches all three sides at one point?

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