Semicircles, Quadrants and Composite Shapes

In short: The perimeter of a semicircle is half the circle's curve plus the straight diameter: $\frac{1}{2}\pi d+d$. A quadrant is a quarter circle, so its perimeter is a quarter of the curve plus two radii. Always remember to add the straight edges.

Before you start

• Circumference of a circle: $C=\pi d$, with $\pi \approx \frac{22}{7}$ or $3.14$ (see Circles and Circumference).
• The diameter is twice the radius.
• Perimeter means the total distance around the outside of a shape.

Semicircles

A semicircle is half a circle. Its perimeter has two parts: the curved arc and the straight diameter.

Quadrants

A quadrant is a quarter of a circle. Its edge is a curved arc plus two radii.

Composite shapes

A composite shape is made of simpler shapes joined together.

Quick summary

• Semicircle perimeter $=\frac{1}{2}\pi d+d$.
• Quadrant perimeter $=\frac{1}{4}\pi d+2r$.
• Always add the straight edges.
• For a composite shape, trace the outside edge and add every piece. Edges inside the shape do not count.
• Two equal semicircles make a full circle of curve, and so do four equal quadrants.

Quiz