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### Course: Class 9 (Old)>Unit 7

Learn to identify quadrilaterals such as kites, trapezoids, parallelograms, rhombuses, rectangles, and squares by side length, presence of parallel sides, and angle type. Created by Sal Khan.

## Want to join the conversation?

• Is a square always a rombus?
• Yes, because a rhombus is a parallelogram with equal sides, and a square is also a parallelogram with equal sides.

The difference is that the square also has four right angles.

Rhombus
- 4 equal sides
- parallelogram

Square
- 4 equal sides
- parallelogram
- 4 equal 90° angles

Notice that the square - by definition - always meets the criteria for a rhombus. So every square is also a rhombus!

However, not every rhombus is a square: if the rhombus has 2 acute angles and 2 obtuse angles, then it is just a rhombus.

Hope this helps!
• Just a quick question that's been on my mind:

Is it possible for any trapezoid to have the pair of parallel sides having equal length? If it did, it would be considered a square, right? But is a square considered a trapezoid? :/
• No. By definition trapezoids will always have only one pair of parallel sides. Having a trapezoid with two parallel sides of equal length would give you two pairs of parallel sides, which would be considered a rectangle instead of a trapezoid. A square will also always have two pairs of parallel sides, and thus cannot be a trapezoid.
• is there any proof that if a parallelogram has one right angle, it's a rectangle?
• Well, the definiton of parallelogram is that both pairs of sides are parallel - what I mean by pairs of sides is tricky to explain without a drawing, so I'm gong to assume you already know it. The diefinition of right angle is a measure of 90 deg, which means the two lines are perpendicular to each other. So with some logic you can see that if one line a is perpendicular to line b, and line c is parallel to line a, then line b has to be perpendicular to c as well. Right? And that means the angle between b and c has to be a right angle as well. You can keep going around the parallelogram and get four right angles, which means it's a rectangle
(1 vote)
• Yeah, quad means 4. To be a quadrilateral, it HAS to have no curves AND be a closed shape.
• is a square always a rhombus ?
• A square is defined as a quadrilateral with 4 equal sides and 4 equal angles.

A rhombus is defined as a quadrilateral with 4 equal sides.

Comparing these definitions, we see that, yes, every square is a rhombus. However, not every rhombus is a square (for example, think of a tall and thin diamond shape).
• i am still confused.for example,at why did you choose like the rhombus instead of the parallelogram.
• He picked rhombus instead of parallelogram because rhombus is the most specific item from the list. The question asks for us to "be as specific as possible" so while it is a parallelogram, that answer would be wrong.
Rhombus is more specific because rhombi are a subset of parallelograms, meaning all rhombi are parallelograms, but not all parallelograms are rhombi. Rhombus is a parallelogram with all equal sides.
• What is a trapezoid and isosceles trapezoid?
• Imagine starting with a triangle and cutting off the top parallel to the base of the triangle. That gives you a trapezoid which could be defined as a quadrilateral with exactly one set of parallel lines. Now if you start with an isosceles triangle with the base being the non-equal side, do the same thing and the two non-parallel sides are also congruent, so you have an isosceles trapezoid.
Trapezoids have different definitions and meanings depending on where you are in the world and which Math definition you choose. In Great Britain, what Americans call a trapezoid is called a trapezium (see http://mathworld.wolfram.com/Trapezium.html for some history), and an alternate definition of exactly one pair of parallel sides is given as AT LEAST one pair of parallel sides which would put all parallelograms under this definition. Sorry for the added confusion, but that is where Math is with the term.
• How come the exercises claim that if every side has the same length, the quadrilateral has to be a rectangle? I was always taught only a square had all four sides of the same length and rectangles had two sets of parallels that differed in length.