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A thali is round. So is a bangle, and so is a temple tank. How long is the rim (outer edge) of each? How much space does each cover?

This is Chapter 6 of your textbook. It is called Measuring Space: Perimeter and Area.

• Way round ÷ way across — one number for every circle.
• Not a fraction — so our values are close, not exact.
• Three old approximations — close values, and how far each one misses.
• An arc — a share of the way round.
• The area inside — thin slices, called wedges, laid in a strip.
• A sector — a slice, with its share of the area.
• Area from three sides — no height needed.
• Four sides on a circle — the triangle is one case.
• A rectangle into a square — same space, drawn.

A quick catch-up

Each idea below has an earlier lesson. Open one for a quick look.

• A slanted edge covers squares in parts. Area still counts unit squares.
• Height meets the base at a right angle. It can lie outside.
• Odd shapes — smaller shapes joined, or one shape taken from another.
• Right triangle. Two short sides, squared and added, equal the longest side squared.
• A slice gets the same share of 360° as of the whole.
• A fixed edge does not fix the space inside.