Step by step
The question
Question: draw the locus of the points that are 4 cm from a point A.
points 4 cm from A
A locus is the set of all the points that follow a rule.
Here: exactly 4 cm from A.
locus = all the points that follow the rule
1 Try some points
Some points 4 cm from A, in different directions.
They all lie on a circle.
2 Draw the locus
Open the compass to 4 cm and draw a full circle around A.
Every point on it is 4 cm from A.
Careful!
The locus is only the circle itself.
Points inside are less than 4 cm away.
Careful: exactly 3 cm = the circle line, not the inside
3 Check
Let's check: measure from A to any point of the circle: 4 cm.
So it is right!
any point on the circle: distance to A = 4 cm
Let's look back.
First: try some points.
Then: draw the locus.
Last: check.
Answer
points 4 cm from A