Foundation and Higher · loci
A locus is every
point that obeys
the rule.
three rules,
three shapes
all the points that fit a rule —
Locus
Latin for place
more than one: loci
rule 1 of 4
From a point: a circle
1. “3 cm from P”: 3 cm in every direction.
2. Set the compass to 3 cm and draw.
✓ A circle, centre P
rule 2 of 4
From a line: a track
1. “2 cm from the line AB” on both sides.
2. Parallel lines, then round the ends.
✓ A running-track shape
rule 3 of 4
Two points: a bisector
1. “The same distance from A and from B.”
2. Draw the perpendicular bisector of AB.
✓ Every point on it is equidistant
putting it together
Combine and shade
1. Within 3 cm of A: inside the circle.
2. Closer to B: right of the bisector.
✓ Shade where both rules are true
loci —
From a line
parallel lines and round ends
From two points
the perpendicular bisector
Leave your construction
arcs in. They earn marks.
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