Any shape with 4 straight sides is a quadrilateral. That is the whole family.
Step 1: Let's Learn
Read it, or press Listen and follow the words.
Members of the family
Squares, rectangles, rhombuses, and trapezoids all have 4 sides.
Categories inside categories
A square has 4 square corners, so it is a rectangle. And it has 4 sides, so it is a quadrilateral too.
One shape, several true names
A square can be called a square, a rectangle, and a quadrilateral. All three are correct.
A family, not a list
A quadrilateral is any shape with four straight sides. Rectangles, squares, rhombuses and trapeziums are all quadrilaterals. They are not separate categories sitting side by side — they are members of one family, some of which are also members of each other.
Every square is a rectangle
A rectangle is a quadrilateral with four right angles. A square has four right angles, so it qualifies — it just also happens to have four equal sides. So every square is a rectangle, but not every rectangle is a square. This surprises most people the first time.
Definitions decide, not appearances
Whether a shape belongs to a category is settled by checking the definition, not by whether it looks typical. A very long thin rectangle is still a rectangle. Learning to test against a definition rather than against a mental picture is a real mathematical habit.
Step 2: Try It Yourself
Tap and try it out.
Square
Straight sides
4
Corners
4
A square has 4 sides that are all the same length.
Turning it does not change what it is.
Rhombus
Straight sides
4
Corners
4
A rhombus has 4 sides that are all the same length.
Turning it does not change what it is.
Step 3: Watch an Example
One step at a time.
Watch Ana Name a Shape Three Ways
Ana is shown a square and asked what it is.
- Step 1
She counts 4 equal sides and 4 square corners, so it is a square.
Step 4: Your Turn
Practice makes it stick.
Is It a Quadrilateral?
Problem 1 of 2
Is a trapezoid a quadrilateral?
The Other Way
Problem 2 of 2
Is every rectangle a square?
Naming the Family
1 of 3
How many sides does a quadrilateral have?
2 of 3
Is a square a rectangle?
3 of 3
Is a rhombus a quadrilateral?
Step 5: Quick Check
Show what you know.
Question 1 of 2
How many sides does every quadrilateral have?
Question 2 of 2
Can one shape have more than one correct name?
What You Learned
- A quadrilateral is any shape with 4 straight sides.
- Squares, rectangles, rhombuses, and trapezoids are all quadrilaterals.
- One shape can have several correct names.