CCSS.Math.Content.4.G.A.2
The standard
Classify two-dimensional figures based on the presence or absence of parallel or perpendicular lines, or the presence or absence of angles of a specified size. Recognize right triangles as a category, and identify right triangles.
Common Core State Standards for Mathematics · Geometry
What this standard means
Students need to sort and name flat shapes by their line and angle features. They should look for parallel sides, perpendicular sides, right angles, acute angles, obtuse angles, and identify triangles with one right angle as right triangles.
Mastery looks like students explaining why a shape belongs in a group, not just naming it. Common trouble spots are mixing up parallel and perpendicular, thinking a tilted right angle is not a right angle, and assuming all triangles with a “square corner” marker are the only right triangles.
Ways to teach it
- Hands-on: Give pairs shape cards, rulers, and index cards labeled parallel, perpendicular, right angle, acute, obtuse, and right triangle for sorting.
- Prompt: Show a rectangle, rhombus, trapezoid, and right triangle, then ask, “Which two belong together and why?”
- Quick assessment: Display six shapes and have students write P, X, R, or RT to mark parallel, perpendicular, right angle, or right triangle.
- Real-world connection: Students photograph or sketch classroom objects, then label any parallel lines, perpendicular lines, and right angles they find.
Plan a lesson for CCSS.Math.Content.4.G.A.2
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Related standards
- CCSS.Math.Content.4.G.A
Draw and identify lines and angles, and classify shapes by properties of their lines and angles.
- CCSS.Math.Content.5.G.B
Classify two-dimensional figures into categories based on their properties.
- CCSS.Math.Content.2.G.A.1
Recognize and draw shapes having specified attributes, such as a given number of angles or a given number of equal faces. Identify triangles, quadrilaterals, pe...
- CCSS.Math.Content.4.G.A.1
Draw points, lines, line segments, rays, angles (right, acute, obtuse), and perpendicular and parallel lines. Identify these in two-dimensional figures.