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### Course: Basic geometry and measurement>Unit 4

Learn about the properties of quadrilaterals, parallelograms, trapezoids, rhombuses, rectangles, and squares. Created by Sal Khan and Monterey Institute for Technology and Education.

## Want to join the conversation?

• In i realized that a rectangle cannot be a square, however a square can be a rectangle. Is this right?
• That is right because a square is a type of rectangle
• At around , Sal goes on about the importance to clarify your definition of trapezoid. Does anyone have any examples of when or why someone would use the broader definition?
• To give one example, let's say that you proved the formula for the area of a trapezoid. Then you could easily find the area of a parallelogram IF you thought that it was a special kind of trapezoid where the two bases had the same length. There are a couple of other small sorts of things like that that could save you a little bit of thought.

As a mathematician, I think that anyone who is really passionate one way or the other about this needs to get out more. :)
• does a rectangle have to have two different pairs of side lengths or can it have 4 lengths that are the same?
• You are correct. Squares are also rectangles.
• What would a hundred sided shape be called a centagon?
• Actually they are called hectogons but centagon would also make sense.
• Which definition of a trapezoid would you guys pick? My choice is at least one pair of parallel. What's yours?
• A 4-sided flat shape with straight sides that has a pair of opposite sides parallel.
• what is the difference between a parallelogram and a trapezium ? :)
• Both parallelograms and trapeziums are quadrilaterals.

Trapeziums have at least one couple of parallel opposite sides. (Some claim it is exactly one couple, but I prefer the broader definition)

Parallelograms have two couples of parallel opposite sides. According to the definition I prefer, all parallelograms are trapeziums ( but not all trapeziums are parallelograms ).
• What do the yellow tick marks/tiny lines on each side of the shape indicate?
• The squares on the corners indicate it is a right angle, meaning a 90 degree angle and the lines on the sides i think indicate if that side is parallel with its opposite side.
• A shape could have as many as a 10000000 sides right?
• There are shapes such as chilikagon with 1000 sides.
And 3d shapes such as myriagon with 10,000 sides.
There can be shapes liked that with 10000 or so sides but I have not heard of anything like that.