Advanced Mathematics Primary 4 Symmetry

Mrs Lee gives her art class a worksheet. On a square grid, only the right half of a figure is drawn, together with a vertical dashed line of symmetry on its left edge. The right half is a rectangle that is 3 squares wide and 2 squares tall. Students complete the figure by reflecting the right half across the dashed line. How many lines of symmetry does the completed figure have?

A 0 lines
B 1 line
C 2 lines
D 4 lines
Show Worked Solution

Worked Solution

Step 1: Determine the completed figure. The right half is 3 squares wide and 2 squares tall. Reflecting across the vertical dashed line produces an equal left half. The completed figure is a rectangle 6 squares wide and 2 squares tall. Step 2: Find all lines of symmetry of the completed rectangle. A non-square rectangle has exactly 2 lines of symmetry: Line 1 — vertical line through the midpoints of the 2-square-tall sides. Line 2 — horizontal line through the midpoints of the 6-square-wide sides. Diagonal lines are NOT lines of symmetry for a non-square rectangle. Answer: 2 lines.

Correct answer: 2 lines

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