Triangle typesBy angles
Name: Date:
Name each triangle.
1 acuterightobtuse
2 acuterightobtuse
3 acuterightobtuse
4 acuterightobtuse
5 acuterightobtuse
6 acuterightobtuse
7 acuterightobtuse
8 acuterightobtuse
Classify triangles by angles worksheets
Name a triangle by its widest corner: every corner under a right angle is acute, one square corner is right, one corner past square is obtuse. These free printable worksheets drill that one naming.
Kid stuck on one? You don’t just get the sheet.
Classify triangles by angles
The answer key prints on a separate page.
What's on this sheet
This is the angle half of the standard, split from the mixed classifying page so a child works one question at a time. Only the biggest angle decides the name, which is the shortcut worth teaching: the other two corners cannot change the answer once the widest is judged.
Why this sheet works
The right triangle carries a small square in its corner and the obtuse triangle has one corner visibly opened past ninety degrees, so the figure supports the judgment rather than hiding it. Nothing needs measuring — this is a looking task, and the drawings are true.
How this one works
One question from this sheet, worked through a step at a time.
Name this triangle
angles:30°30°120°
angles:30°30°120°
angles:30°30°120°
obtuse
- Every triangle has TWO names — one for its angles and one for its sides — and it has both at once. This question is asking for the ANGLE name, so look only at the angles.
- Classify by the BIGGEST angle — it is the only one that can be a right angle or wider, so it alone decides the type. Here that is 120°.
- More than 90, so it is OBTUSE. One obtuse angle is all it takes — and a triangle can never have two.