Classifying Triangles by Sides and Angles Worksheets for 4th Grade

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Grade 4MathMeasurement & GeometryCCSS 4.G.A.2

Skill: Classifying triangles as acute, right or obtuse and as equilateral, isosceles or scalene

Preview of the Classifying Triangles by Sides and Angles printable worksheet
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Teaching tips and what to try next

Aimed at fourth graders who can already sort single angles in Classify Angles: Acute, Right or Obtuse. A folded square corner helps test for a right angle before naming the triangle. Side classification needs careful reading of the three lengths, and lines and rays are reviewed in Lines, Rays and Line Segments.

10 versions, each with its own answer key

Same skill and layout, a fresh set of problems in every version, so children can keep practicing without repeating a page. Problems are not repeated between versions unless a skill has only a small number of possible problems (for example, the addition facts within 10).

Download all 10 versions (one PDF)All 10 answer keys (PDF)

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About this worksheet

Triangles can be sorted in two useful ways: by their angles and by their sides. An acute triangle has three acute angles, a right triangle has one right angle, and an obtuse triangle has one obtuse angle. By sides, a triangle may be equilateral, isosceles or scalene. Fourth graders are expected to classify figures by angles and related properties, and this fourth grade worksheet practices both sorts.

The page has twelve triangles. In Part A, six triangles ask children to write acute, right or obtuse from the shape of the angles. In Part B, six triangles show side lengths, and children write equilateral, isosceles or scalene. A short reminder at the top reviews the six words. Each of the ten versions has new triangles and its own answer key.

How to use it: for Part A, have your child compare each angle to a square corner made with a folded piece of paper. For Part B, read the three side lengths out loud and ask how many match. A right isosceles triangle can appear in either part depending on what the question asks, so reading the direction matters.

The answer key names every triangle. For sorting single angles first, try our Classify Angles: Acute, Right or Obtuse worksheet. For the building blocks of geometry, try our Lines, Rays and Line Segments worksheet.