Fourth graders discover that every triangle can be named two ways, by its sides and by its angles, and explore the six categories so they can describe any triangle they meet.
Students will be able to…
Every triangle has three sides and three angles, yet they come in many shapes. What are the two ways mathematicians sort triangles into groups?
Project this and open each card to explore a type of triangle, sorted by its sides or by its angles.
Tap any phase to open the teacher moves and student actions.
Every triangle has three sides and three angles, yet a tall thin one and a wide flat one look nothing alike. How can we sort them into groups?
Students explore the types of triangles.
Students give each triangle two names.
Students build a sorting chart.
Students reflect on classifying triangles.
Aligned to the Common Core State Standards for Mathematics.
Classify two-dimensional figures based on the presence or absence of angles of a specified size; recognize right triangles as a category.
Draw points, lines, line segments, rays, angles (right, acute, obtuse), and identify these in two-dimensional figures.
Understand that shapes in different categories may share attributes and that the shared attributes can define a larger category.
Look for and make use of structure.
Preview the three formative checks. Tap “Sample answer” to see what mastery looks like — hide them before you print for students.
Have students draw or cut out six triangles, sort them once by sides and again by angles, and label each group, so the two ways of classifying become clear. A printable triangles worksheet is in the Mathematics library.
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A quick self-check with instant feedback, drawn from this lesson’s key terms.
A print-and-go review sheet with a built-in answer key. Tap “Show answer key” to reveal answers, or print the clean version for students.