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Depth 1 · 90 s

A family of four sides

Six four-sided shapes, each named by its rule - and why a square is a rectangle and a rhombus at once. Plus the 360 degrees inside every one.

About this video

Every shape with four straight sides is a quadrilateral, but some have names of their own, and each name is a rule. This animation draws the six you meet most. A rectangle has four right angles. A square has four right angles and four equal sides. A parallelogram has two pairs of parallel sides, marked with matching arrows. A rhombus has four equal sides, like a square pushed over. A trapezium (called a trapezoid in the US) has just one pair of parallel sides. And a kite has two short sides next to each other and two long ones next to each other.

Then the question that trips people up: is a square a rectangle? Check the rule. A rectangle needs four right angles, and a square has them, so yes. A rhombus needs four equal sides, and a square has those too, so it is a rhombus as well. Every square is a rectangle in the same way every cat is an animal, while not every rectangle is a square. The family tree shows it: each name keeps every rule of the names above it.

Last, one diagonal cuts any quadrilateral into two triangles. The angles of each triangle add up to 180 degrees, so the four corners of every quadrilateral add up to 360. This video goes with the Four-Sided Shapes lesson of Geometry Level 1 on Knaph.

This video shows depth 1 of Quadrilaterals.

Learn Quadrilaterals

Transcript

  1. 0:00Four straight sides. But they come with six different names.
  2. 0:06A rectangle has four right angles.
  3. 0:12A square has four right angles, and four equal sides.
  4. 0:17A parallelogram has two pairs of parallel sides.
  5. 0:23A rhombus has four equal sides. A square, pushed over.
  6. 0:28A trapezium has just one pair of parallel sides.
  7. 0:34And a kite. Two short sides together, two long sides together.
  8. 0:40So, is a square a rectangle?
  9. 0:44It has four right angles. So yes, it is a rectangle.
  10. 0:49And four equal sides. So it is a rhombus too.
  11. 0:56Every square is a rectangle, the way every cat is an animal.
  12. 1:02Each name keeps every rule of the names above it.
  13. 1:08Draw one diagonal, and any four-sided shape becomes two triangles.
  14. 1:15Each triangle makes 180. Two of them make 360.
  15. 1:22The four corners always add up to 360 degrees.