L1 · Reflection symmetry
“I can check whether a shape has reflection symmetry by folding or mirroring it, I can find and count its lines of symmetry, and I can complete a shape across a mirror line on a grid.”
Does the letter A have reflection symmetry? Step 1: Imagine a vertical line down the middle of the A. Step 2: Fold along that line. The left half lands exactly on the right half - every edge matches, nothing sticks out. Step 3: Because the fold makes the halves coincide, A HAS reflection symmetry, and the fold line is a line of symmetry. Counting lines: a square passes this test 4 ways - vertical, horizontal, and both diagonals. A rectangle passes only 2 ways: its diagonals do NOT work, because folding a rectangle corner-to-corner leaves edges sticking out.
A shape has reflection symmetry when...
Does the letter H have a HORIZONTAL line of symmetry? -> Yes - folding top-to-bottom makes the halves match, so H has both a vertical and a horizontal line of symmetry (2 in total).
"An equilateral triangle: fold along the line from one vertex to the middle of the opposite side. The halves match, so that line is a ___" -> line of symmetry (an equilateral triangle has 3 lines of symmetry in total)
10 scored questions with a 3-rung hint ladder. Mastery needs 8/10 plus both gate questions.