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**rajinikanth0602****Member**- Registered: 2012-06-30
- Posts: 16

can any one say the angle between the planes in a pentagon ball???????

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**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 7,020

hi rajinikanth0602

Yes, I expect someone can. But shouldn't you respond to

http://www.mathisfunforum.com/viewtopic.php?id=18761

first?

Bob

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

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According to wikipedia, and what I understood, such a solid is a dodecahedron.

And the requied angle is 116.57°.

I shall be waiting eagerly for someone to explain why

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

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**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 7,020

hi Agnishom,

I've done a few of these over the last two years. The method uses vector geometry and the cosine rule. See

http://www.mathisfunforum.com/viewtopic.php?id=16061

Post 30.

I think Wiki also gives the co-ordinates of the points in 3D so you can pick two adjacent faces, get the critical lines and apply the method.

I've got a post to make for MIF, so It'll be a while before I can put all the figures to this, so have a go yourself.

Bob

ps. I have a vague memory that I have done it in a thread, but I couldn't find it.

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

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