Lines of Symmetry
Aligned to 4.G.A.3 — Common Core State Standards for Mathematics.
What this lesson teaches
A line of symmetry is a fold line: if you fold a shape along it, both halves match exactly. Some shapes have no line of symmetry, some have one, and some have many.
Worked example
Take a square. Fold it straight down the middle and the two halves match, so that is a line of symmetry. You can also fold it across, and along both diagonals. A square has 4 lines of symmetry in all.
Practice questions
- How many lines of symmetry does a rectangle (not a square) have?
- Draw a triangle with all equal sides and show its lines of symmetry.
- Is the letter H symmetric? Draw any lines of symmetry it has.
Watch the lesson
Every lesson comes with a video taught in English and Spanish — the same video the QR code in the printed workbook opens.
▶ Watch this lessonEn español
Ejes de simetria
Un eje de simetria es una linea de doblez: si doblas una figura por ella, las dos mitades coinciden exactamente. Algunas figuras no tienen ningun eje de simetria, otras tienen uno y otras tienen muchos.
Ejemplo: Toma un cuadrado. Doblalo justo por la mitad y las dos mitades coinciden, asi que ese es un eje de simetria. Tambien puedes doblarlo de lado y por las dos diagonales. Un cuadrado tiene 4 ejes de simetria en total.
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