Cogito
Grade 4 Math · Chapter 7 · Lesson 6
Lines of Symmetry
A fold that makes both halves match.
10 problems · about 14 minutes · 4.G.A.3
What this lesson teaches
The child identifies lines of symmetry in two-dimensional figures.
- A line of symmetry splits a shape into matching halves.
- Folding is the test.
- Some shapes have many, and some have none.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — Sorting Shapes by Their Angles: How many right angles can a triangle have?
Answer 1
Why Two right angles would use all 180 with nothing left.
Review — Lines, Rays, and Segments: At how many degrees do perpendicular lines cross?
Answer 90
Why 90 degrees.
Warm Up
Straightforward practice. Get the method working first.
4 problemsHow many lines of symmetry does a square have?
Answer 4
Why 4 lines.
How do you test a line of symmetry?
Answer Fold along it and see if the halves match.
Why Folding is the test.
How many lines of symmetry does a rectangle have?
Answer 2
Why Not the diagonals.
How many lines of symmetry does an equilateral triangle have?
Answer 3
Why One through each corner.
Build It Up
The same ideas with more to keep track of.
2 problemsHow many lines of symmetry does the letter H have?
Answer 2
Why Across and down.
Does every shape have a line of symmetry?
Answer No.
Why Some folds never match.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Square: How many lines of symmetry does a square have?
Answer 4 lines
Why 4 lines.
The Letter: How many lines of symmetry does the letter A have?
Answer 1 lines
Why 1 vertical line.