Math Is Fun Forum
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#1 2012-11-05 01:07:11
Those inequalities again
Prove that in a quadrilateral ABCD,
AB + BC + CD > DA
'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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#2 2012-11-05 01:14:37
- Bob
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Re: Those inequalities again
hi
Split your quadrilateral into two triangles and use the triangle inequality twice.
Bob
Children are not defined by school ...........The Fonz
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Sometimes I deliberately make mistakes, just to test you! …………….Bob 
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#3 2012-11-05 01:25:36
Re: Those inequalities again
Tried...But how do I get rid of the diagonal in the equation?
'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'
I'm not crazy, my mother had me tested.
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#4 2012-11-05 01:39:44
- anonimnystefy
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- From: Harlan's World
- Registered: 2011-05-23
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Re: Those inequalities again
You can do it like this:
CD<AC+AD<(AB+BC)+AD. Q.E.D
Last edited by anonimnystefy (2012-11-05 01:40:45)
Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.
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#5 2012-11-05 02:40:53
Re: Those inequalities again
Yes! Thanks to bob bundy and anonimnystefy
'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'
I'm not crazy, my mother had me tested.
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#6 2012-11-05 02:43:35
- anonimnystefy
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- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,049
Re: Those inequalities again
You are welcome!
Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.
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