Foundation and Higher · perimeter
Perimeter: the
distance all the
way round.
find the missing
sides first
a circle’s perimeter has its own name —
Circumference
C = πd
pi times the diameter
step 1 of 4
Find the missing sides
1. Opposite sides match: 10 across, 8 up.
2. Go round once, adding every side.
✓ Six sides, six numbers
10 − 4 = 6 8 − 5 = 3
10 + 5 + 6 + 3 + 4 + 8
perimeter = 36 cm
step 2 of 4
Circumference
1. The diameter goes right across.
2. Use the π button, not 3.14.
✓ 8π cm is the exact answer
step 3 of 4
Given the radius?
1. The radius only goes halfway.
2. Double it for the diameter first.
✓ Or use C = 2πr
d = 2 × 5 = 10
C = π × 10
= 31.4 cm
step 4 of 4
Semicircle: two parts
1. The curved part is half a circumference.
2. Then add the straight edge.
✓ Do not forget the straight edge
arc = 12 × π × 8 = 12.57
straight edge = 8
perimeter = 20.6 cm
perimeter and circumference —
Perimeter
add every side, once
Circumference
π × diameter
Part circles
add the straight edges
Perimeter is a length:
cm, never cm².
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