A shape is named by what it has, not by which way up it is.
Step 1: Let's Learn
Read it, or press Listen and follow the words.
Triangles by angle
A triangle with a right angle is a right triangle. One with an obtuse angle is obtuse.
Four-sided shapes
A rectangle has 4 right angles. A trapezoid has one pair of parallel sides.
A shape can have two names
Every square is also a rectangle, because it has 4 right angles too.
Properties decide the name
A shape is a rectangle if it has four sides and four right angles — not because it looks like one. Classification means testing against a definition, which is why you must know what each name requires before you can sort anything.
Triangles by their angles
A right triangle has one right angle. An acute triangle has all three angles acute. An obtuse triangle has one obtuse angle. A triangle can have at most one angle of 90° or more, since the three must total 180°.
Triangles by their sides
Equilateral means all three sides equal, isosceles means at least two equal, scalene means none equal. A triangle has both a side name and an angle name, so a shape can be an isosceles right triangle. The two classifications are independent.
Categories overlap
A square is a rectangle, a rhombus, a parallelogram and a quadrilateral all at once. Shape categories nest inside each other rather than sitting side by side, which is exactly what makes sorting them a thinking exercise rather than a labelling one.
Step 2: Try It Yourself
Tap and try it out.
Trapezoid
Straight sides
4
Corners
4
A trapezoid has 4 sides, and 2 of them never meet.
Turning it does not change what it is.
Step 3: Watch an Example
One step at a time.
Watch Ana Name a Triangle
Ana is shown a triangle with one square corner.
- Step 1
She checks the corners for a right angle.
Step 4: Your Turn
Practice makes it stick.
The Square
Problem 1 of 2
Is every square also a rectangle?
The Triangle
Problem 2 of 2
How many right angles can a triangle have?
Sort by Property
1 of 4
How many right angles does a rectangle have?
2 of 4
How many pairs of parallel sides does a rectangle have?
3 of 4
Is every rectangle also a square?
4 of 4
Does turning a shape change its name?
Step 5: Quick Check
Show what you know.
Question 1 of 2
How many right angles can a triangle have?
Question 2 of 2
What names a shape?
What You Learned
- Shapes are named by their properties.
- A triangle can have at most one right angle.
- Every square is a rectangle, but not the other way round.