Learn · Illustrative Mathematics K–5 · Grade 4 · Unit 8
Short lessons you can play with. Name triangles by their sides and angles, sort quadrilaterals by what they have, fold shapes to find lines of symmetry, and use what a shape has to find lengths, then check yourself.
Four short chapters follow the unit’s lessons in order. Each step shows one idea with something to tap or move, then a quick check. A wrong answer names the likely mistake and gives one more try. Progress is saved on this device.
Shapes use the marks from class: tick marks on sides that are the same length, and small boxes on right angles. Lines of symmetry are dashed, and folding a shape shows its outline flipped over the fold.
Equilateral, isosceles, scalene: triangles with 3, at least 2, or no equal sides. Acute, right, obtuse triangle: named by its biggest angle. Parallel sides: sides that go the same way and never meet. Line of symmetry: a fold line that makes the two halves match.
All Kinds of Attributes (Lesson 6), Symmetry in Action (Lesson 9), and Ways to Find Angle Measurements (Lesson 10) are optional lessons. Practice it all in Shape Gallery, the game for this unit.