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## Geometry (FL B.E.S.T.)

### Course: Geometry (FL B.E.S.T.)>Unit 5

Lesson 5: Theorems concerning quadrilateral properties

# Proof: Rhombus area

Sal proves that we can find the area of a rhombus by taking half the product of the lengths of the diagonals. Created by Sal Khan.

## Want to join the conversation?

• in a rhombus, are the angles alwyas right angles?
• No, a rhombus only means that all the sides are of equal length. A Square, is a Rhombus where all the sides intersect at right angles.
The diagonals of a Rhombus, however, do always intersect at right angles.
• How do you remember the meaning of all the shapes? For example:
- Rhombus
- Kite
- Square
- Rectangle
and so on...
• Try to link the shapes with what you know and your environment. Like, a rhombus looks like someone had sat on a square slightly, the kite would be like a square but tilted forward while a square is taking two 'L's together and putting them on top on each other.
• The plural of rhombus is rhombi, but how does one know which words to say "uses" and which words to say "i"? I've always wondered that.
• Good question. It will depend of which language the word is taken from. Rhombus comes from the greek rhombos. It was then used in latin as rhombus. The plural of a -us word in latin is -i. Sometimes, a foreign word will be anglicized and it will lose its weird (for us) plural form. Language, like mathematics, is conventions that were agreed upon at one point in history and is not always logical. ;)
• But what if it asked a question like "Find the area of rhombus when a side and diagonal are given"
Like when a diagonal is 12 and side is 10 ?
• Since the diagonals of a rhombus are perpendicular, you can use the Pythagorean theorem to find the other diagonal and then find the area.
• whats the difference between perpendicular and parelel?
• For example parallel lines have the same slope and different y intercepts, while a perpendicular line is the negative reciprocal of the other slope.In shapes now parallel lines are basically opposite of each other and don't intersect.While perpendicular lines always for right angles or 90 degree angles.
• don't you think they should try something harder like a parallelogram?
• I think Sal is trying to cover every angle of this topic so thats why he would use a rhombus and he covers the area of a parallelogram in the next video
• Where did you get the 1\4 in the rhombus area video