Curriculum placement
Grade 4. This describes the skill, not a learner estimate.
Parallel lines, perpendicular lines, and symmetry
Identify parallel perpendicular and symmetric features
Problem types
- Acute, right or obtuse
- Lines, rays and segments
- Parallel or perpendicular
- Triangles by their angles
- Count lines of symmetry
- Find the line of symmetry
- Classify a triangle by sides and angles
- Name a quadrilateral from its marks
- Select shapes by their sides or angles
- Select the two lines that are parallel or perpendicular
- Select the angles that are acute, right or obtuse
- Select the figures with a correct line of symmetry
Builds on
Leads to
- Precise definitions in geometry
- Measuring angles · Extend the idea
Telling acute, right and obtuse angles by comparing with a square corner comes before measuring them. A protractor reading then puts a number on the same comparison.
- Symmetries of a polygon · Extend the idea
A line of symmetry is a reflection that maps a polygon onto itself, so counting lines of symmetry counts some of its symmetries.
Related skills
- Categories and subcategories of shapes · Related idea
The number of lines of symmetry separates shapes in the hierarchy: a square has four and a rectangle has two.
- Halves and quarters of a whole · Related idea
A line of symmetry splits a shape into two equal halves that match.
- Translations, reflections, and rotations · Related idea
Reflecting a shape across its line of symmetry is a rigid motion that maps the shape onto itself.
- Shifts, stretches, and reflections of graphs · Related idea
A graph symmetric about the y-axis has a line of symmetry, and this is what makes a function even.
- Sides, angles, and faces · Shared foundations
Open the interactive map to explore lessons and skill connections.