Every triangle has 3 sides and 3 angles that always sum to 180°. But within that rule, triangles come in several flavours.
By sides: An equilateral triangle has all three sides equal — and all angles are 60°. An isosceles triangle has exactly two equal sides, and the angles opposite those sides are equal. A scalene triangle has all three sides different.
By angles: An acute triangle has all angles less than 90°. A right triangle has exactly one 90° angle. An obtuse triangle has one angle greater than 90°.
A triangle can be both isosceles and right — these classifications work together, not against each other.
Remember
Equilateral → all equal. Isosceles → two equal. Scalene → none equal. These describe the sides, not the angles.
Real World
A roof truss is often a triangle because triangles are rigid — they don't flex or collapse the way rectangles can. Builders love them for strength.
Feeling ready?
Put this concept to work with a practice workout.