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# help.

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What is a radian and what is the plural form of radius cause I was watching khanacademy and he said radiuseseseses so I'm confused.

Oct 8, 2017

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What is a radian and what is the plural form of radius cause I was watching khanacademy and he said radiuseseseses so I'm confused.

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For me the plural of radius is radii  BUT  my country (Australia) uses the same versoin of English as England does.

The USA has changed much of the spelling to make it easier. So maybe for them the plural of radius is radiuses.

A USA person will need to comment on this.

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The circumference of a circle is  $$2\pi r$$

And there are  $$2\pi$$  radians in a revolution.

so                      $$\boxed{2\pi\;\;radians\;\;=\;\;360^\circ}$$

Rearranging this equations we get.

$$2\pi\;\;radians\;\;=\;\;360^\circ\\ 1\,radian=(\frac{180}{\pi})^\circ\\ or\\ 1^\circ=\frac{\pi}{180}\;radians\\$$

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Oct 8, 2017
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Just looked through a few on-line American dictionaries.  They all use radii for the plural of radius.

Alan  Oct 8, 2017
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Here is one that uses radiuses

https://goo.gl/WpaFNp

Melody  Oct 8, 2017
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Alright, then he must have accidentally said it wrong. I thought so at first because radiuseseseses sounded very incorrect but then he said the same thing twice so I got very confused. Thanks!

ISmellGood  Oct 8, 2017