Quadrilateral facts for kids
Quick facts for kids Quadrilateral |
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|---|---|
Some types of quadrilaterals
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| Edges and vertices | 4 |
| Schläfli symbol | {4} (for square) |
| Area | various methods; see below |
| Internal angle (degrees) | 90° (for square and rectangle) |
In flat geometry, a quadrilateral is a shape with four straight sides and four corners. Think of it like a four-sided polygon. You might also hear it called a quadrangle, which is similar to how we say triangle for a three-sided shape. Another name is tetragon, which fits with names like pentagon (five sides) and hexagon (six sides).
The word "quadrilateral" comes from Latin. "Quadri" means four, and "latus" means side. So, it literally means "four sides."
Some quadrilaterals are "simple," meaning their sides don't cross each other. Others are "complex" or "crossed," which means their sides do cross. Simple quadrilaterals can be either "convex" (all corners point outwards) or "concave" (at least one corner points inwards).
Interestingly, if you have a quadrilateral whose sides don't cross, you can often use copies of it to completely cover a flat surface without any gaps or overlaps. This is called "tiling the plane."
Contents
What is a Quadrilateral?
A quadrilateral is a basic shape in geometry. It's a type of polygon, which is a closed shape made of straight lines. Every quadrilateral has:
- Four straight lines, called sides or edges.
- Four points where the sides meet, called vertices or corners.
Different Kinds of Quadrilaterals
Quadrilaterals come in many forms. They can be simple or complex.
Simple Quadrilaterals
Simple quadrilaterals are the ones you see most often. Their sides do not cross each other. They can be:
- Convex: All the corners point outwards. If you draw a line between any two points inside a convex quadrilateral, the line will always stay inside the shape. Most common quadrilaterals like squares, rectangles, and trapezoids are convex.
- Concave: At least one corner points inwards, like a dent. If you draw a line between two points inside a concave quadrilateral, part of the line might go outside the shape.
Complex Quadrilaterals
Complex quadrilaterals are also called "crossed" quadrilaterals. Their sides cross over each other. They look a bit like a bow tie or an hourglass.
Quadrilaterals in Everyday Life
You see quadrilaterals everywhere!
- Buildings: Most windows, doors, and even the walls of rooms are rectangular or square.
- Screens: Your phone, tablet, computer, and TV screens are usually rectangles.
- Signs: Many road signs, like stop signs (octagons, but many others are rectangular) and warning signs, are quadrilaterals.
- Books and Papers: The pages of books and sheets of paper are rectangles.
- Sports Fields: Football fields and basketball courts are large rectangles.
Understanding quadrilaterals helps us describe the world around us and is a key part of learning about shapes in mathematics.
More Pictures
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An antiparallelogram
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The (red) side edges of a tetragonal disphenoid represent a regular zig-zag skew quadrilateral
See also
In Spanish: Cuadrilátero para niños
