Discussion about math, puzzles, games and fun.   Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫  π  -¹ ² ³ °

You are not logged in.

## #1 2012-11-05 01:07:11

Agnishom
Real Member
From: Riemann Sphere
Registered: 2011-01-29
Posts: 24,859
Website

### 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'
I'm not crazy, my mother had me tested.

Offline

## #2 2012-11-05 01:14:37

bob bundy
Administrator
Registered: 2010-06-20
Posts: 8,452

### 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
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob Bundy

Offline

## #3 2012-11-05 01:25:36

Agnishom
Real Member
From: Riemann Sphere
Registered: 2011-01-29
Posts: 24,859
Website

### 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.

Offline

## #4 2012-11-05 01:39:44

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,039

### 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.

Offline

## #5 2012-11-05 02:40:53

Agnishom
Real Member
From: Riemann Sphere
Registered: 2011-01-29
Posts: 24,859
Website

### 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.

Offline

## #6 2012-11-05 02:43:35

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,039

### 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.

Offline

## Board footer

Powered by FluxBB