SATS How To...
Welcome to the all new SATS How-to page. Here we will teach you valuble techniques that can be applied in your Maths, English & Science SATS exams, whatever the level. Forgotten how to convert a fraction? Unsure about how to plan an essay? Then the SATS How-to is for you!
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| how to use a 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 and 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.
Solution:
Step 1: Use a ruler to set the distance from the point of the compass to the pencil's lead at 4 cm.
Step 2: Place the point of the compass at the centre of the circle.
Step 3: Draw the circle by turning the compass through 360º.
Activity 1
1. Use a compass to draw a circle of radius 5 cm.
2. Use a compass to draw a circle of diameter 12 cm.
3a. Use a compass to draw a circle of radius 4.5 cm.
3b. Draw the diameter of the circle; and use a ruler to measure the length of the diameter.
3c. Write an equation to represent the relation between the radius, r, and the diameter, d.
4a. Use a compass to draw a circle of radius 5.5 cm.
4b. Draw a diameter and label it PQ.
4c. Draw a triangle PQR where R is on the semicircle.
4d. Use a protractor to measure the size of angle PRQ.
5a. Use a compass to draw a circle of radius 6.5 cm.
5b. Draw a diameter and label it PQ.
5c. Draw a triangle PQR where R is on the semicircle.
5d. Use a protractor to measure the size of angle PRQ.
6a. Use a compass to draw a circle of radius 7.5 cm.
6b. Draw a diameter and label it PQ.
6c. Draw a triangle PQR where R is on the semicircle.
6d. Use a protractor to measure the size of angle PRQ.
7. Use the results of questions 4, 5 and 6 to complete the following statements:
a. The size of the angle on the diameter of a circle with a vertex on the circle is …
b. If a triangle is drawn in a semicircle using the diameter as an edge, the angle touching the curved part of the triangle is …
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