L3 · Symmetry in Shapes and Design: Clinic
“I can use the regular-polygon rule (equal sides = lines of symmetry = order of symmetry), I know a circle has infinitely many lines of symmetry and infinite order, I can compare a shape's symmetry counts with its equal sides and angles, and I can classify shapes by their symmetry and recognize symmetry in nature and in First Nations, Métis and Inuit designs.”
A regular pentagon: 5 equal sides, 5 equal angles. Step 1: Fold test. A line from each vertex to the midpoint of the opposite side makes the halves match - that is one working fold per vertex: 5 lines of symmetry. Step 2: Turn test. The smallest turn moves each vertex to the next vertex: 360 / 5 = 72°, and the shape overlaps 5 times in a full turn - order 5. Step 3: Notice the pattern. Regular hexagon (6 equal sides): 6 lines, order 6. Regular octagon (8): 8 lines, order 8. For a regular polygon, the number of lines of symmetry and the order of symmetry both equal the number of sides - and the number of equal angles is that same number too. One count gives you all three. Step 4: The rule needs the word REGULAR. An isosceles triangle has 2 equal sides but only 1 line of symmetry and no rotation symmetry - equal sides alone do not set the counts; for non-regular shapes, run the fold and turn tests. Say it plainly: regular polygon -> count the sides once and you know both symmetry numbers. Anything else -> test, don't guess.
The regular-polygon rule works because…
A regular hexagon tile: state its lines of symmetry and its order of symmetry. -> 6 lines; order 6.
"A regular polygon has 9 equal sides. Its lines of symmetry number ___, and its order of symmetry is ___." -> 9; 9
10 scored questions with a 3-rung hint ladder. Mastery needs 8/10 plus both gate questions.