Perimeter — O/L Mathematics

What must I remember about Perimeter?

• Perimeter is the total boundary distance enclosing a two-dimensional closed figure.
• Arc length of a sector of radius r and centre angle θ° is given by s = (θ / 360) × 2πr = (θπr / 180).
• Total perimeter of a sector includes both radii plus the curved arc: P = s + 2r = (θ / 360) × 2πr + 2r.
• Standard sector boundaries: Semi-circle (θ = 180°) arc = πr, perimeter = πr + 2r; Quadrant (θ = 90°) arc = (πr / 2), perimeter = (πr / 2) + 2r.
• Compound shape boundaries: Sum only the exposed exterior boundaries; never add interior dividing seams or shared contact edges.

Test yourself (1 minute)

1. The missing radius trap

   The perimeter of a sector is the arc length plus both radii — leave out +2r and the figure you have given is the arc alone.

2. Compound shape internal lines

   Shaded or dashed internal boundaries must strictly be excluded from perimeter calculations.

3. Value of π

   Use π = 22/7 when radius or diameter is a multiple of 7; otherwise use the specified value and state exact units (cm, m).

Practise Perimeter questions today

Source: NIE G.C.E. (O/L) Mathematics Syllabus (Grade 10, Unit 1)

What comes next?

Next in the syllabus

Where does Perimeter fit in the syllabus?

Grade 10 · Term 1