Classifying triangles by sides (equilateral, isosceles, scalene) and by angles (right-angled, acute, obtuse).
Where your child meets this in real life: Identifying triangle types in structures, art, and design
SEAGReady breaks classify triangles into 3 steps, taught in order so each skill builds on the last.
Classify triangles as equilateral, isosceles, or scalene based on the number of equal sides
Classify triangles as right-angled, acute, or obtuse based on their largest angle
Describe triangles using both side and angle classifications together (e.g., 'right-angled isosceles')
Three free sample questions from our classify triangles course. Every question comes with a full explanation, and hints that guide without giving the answer away.
Ciara has a triangular tile with sides measuring 7 cm, 7 cm, and 10 cm. What type of triangle is this?
Answer: B. Isosceles
Count the equal sides: - 7 cm and 7 cm are equal (2 sides) - 10 cm is different Exactly 2 equal sides = isosceles triangle
Stuck? Start here: Count how many sides have the same length.
A triangular bracket has angles of 40 degrees, 50 degrees, and 90 degrees. What type of triangle is this?
Answer: B. Right-angled
The angles are 40, 50, and 90 degrees. The largest angle is 90 degrees. 90 degrees = right angle A triangle with a right angle is a right-angled triangle.
Stuck? Start here: Look at all three angles: 40, 50, and 90 degrees.
A triangle has sides 5 cm, 5 cm, and 5 cm. All angles are 60 degrees. Give the full classification of this triangle.
Answer: A. Acute equilateral
Classify by sides: - 5 cm, 5 cm, 5 cm = all equal = equilateral Classify by angles: - 60, 60, 60 = all less than 90 = acute Full classification: acute equilateral
Stuck? Start here: First classify by sides: How many equal sides? (5, 5, 5)
This is the exact interactive worked example your child sees in SEAGReady. Step through it and watch the method build up.
Niamh is sorting triangular tiles for an art project. One tile has sides measuring 5 cm, 5 cm, and 8 cm.
What type of triangle is this tile?
5 cm, 5 cm, 8 cm
Step 1 of 5
Niamh is sorting triangular tiles for an art project. One tile has sides measuring 5 cm, 5 cm, and 8 cm.
What type of triangle is this tile?
The tile is an isosceles triangle because it has exactly 2 equal sides.
The key insight: Count the matching sides: 3 equal = equilateral, 2 equal = isosceles, 0 equal = scalene!
Watch out: Calling it equilateral because two sides match. Equilateral means ALL three sides are equal, not just two.
These are the misconceptions we see most often in classify triangles, including the ones our practice questions are specifically designed to catch.
Struggling with classify triangles? The real gap is often in one of these earlier topics.
SEAGReady finds the exact step where your child gets stuck, teaches it with worked examples like the one above, and brings it back for review so it sticks.