A formula is a rule in letters

A ribbon goes round the edge of a hexagon. Each side is 7 cm. How long is the ribbon?

Slide the number of sides. Six sides give 6a. Eight sides give 8a.

A hexagon has 6 sides, each 7 cm. The ribbon is the perimeter: the length all the way round. So it is 6 × 7 = 42 cm.

The rule

A formula is a rule written in letters. A regular polygon has equal sides and equal angles. With n sides of length a, its perimeter is n × a.

For the ribbon, 6a is 6 × a. With a = 7, that is 6 × 7 = 42 cm.

One formula gives an answer for every side length. Change a, and the answer changes with it.

Try the lab to finish this lesson.