A short lesson on classifying triangles, in three sheets. The first shows the three names that come from the sides, the three that come from the angles, and how the two fit together. The second is guided practice that takes one kind of name at a time. The third is practice on its own, with an answer key.
The three side names, the three angle names, and a chart of every way the two can go together.
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Name twelve triangles: first by sides, then by angles, then both. The first of each kind is done. Includes answer key.
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Six triangles to name both ways, six always, sometimes or never questions, two to draw and one mistake to explain.
Download PDFEvery triangle has two names. One comes from its sides and one comes from its angles. Students often learn the six words as a single list and then mix them up. It is easier to keep them as two separate questions: how many sides match, and how big is the biggest angle?
The How It Works sheet takes the questions one at a time. By sides, a triangle is equilateral (all three sides the same length), isosceles (two the same) or scalene (none the same). By angles, it is acute (all three angles smaller than a right angle), right (one right angle) or obtuse (one angle bigger than a right angle).
The chart in the third part puts the two names together. It shows seven kinds of triangle, such as a right isosceles triangle or an obtuse scalene triangle. It also shows the two that cannot be made. Every angle of an equilateral triangle is 60°, so an equilateral triangle is never right and never obtuse.
The guided practice sheet asks for the side name only, then the angle name only, then both. The independent practice sheet turns the triangles in different directions, because many students think a right triangle has to sit on its right angle. The types of quadrilaterals lesson does the same job for four-sided shapes, and a printable protractor is useful for checking angles.