A line of symmetry, a basic geometric concept, divides a shape into two identical sections. Teachers introduce the basic concept as early as elementary school, and high school and even college geometry classes employ symmetry. Finding a line of symmetry can be useful in designing objects from greeting cards to landscaping projects.
Things You'll Need
 Ruler
 Pencil
 Mirror

Look for a midpoints in the shape. If you are considering a larger area like a yard, measure the area and draw it to scale on a piece of graph paper to look for midpoints.

Use a ruler to draw a straight line from the estimated midpoint through the shape.

Fold the shape in half to see if both sides match. If they do match, you have found a line of symmetry.

Check all the angles of a shape (if it contains angles) to look for all possible lines of symmetry.

Hold a small mirror perpendicular to a possible line of symmetry. If the shape in the mirror matches the shape on the paper, you have found a correct line of symmetry.
Tips & Warnings
 Some shapes can have multiple lines of symmetry, while some irregular shapes have no lines of symmetry.
References
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