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

Login

Username

Password

Not registered yet?

#1 2012-11-06 00:07:11

Agnishom
Real Member
Award: Wink Sherlock

Offline

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'
'Who are you to judge everything?' -Alokananda

#2 2012-11-06 00:14:37

bob bundy
Moderator

Offline

Re: Those inequalities again

hi

Split your quadrilateral into two triangles and use the triangle inequality twice.

Bob


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

#3 2012-11-06 00:25:36

Agnishom
Real Member
Award: Wink Sherlock

Offline

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'
'Who are you to judge everything?' -Alokananda

#4 2012-11-06 00:39:44

anonimnystefy
Real Member

Online

Re: Those inequalities again

You can do it like this:

CD<AC+AD<(AB+BC)+AD. Q.E.D

Last edited by anonimnystefy (2012-11-06 00:40:45)


The limit operator is just an excuse for doing something you know you can't.
“It's the subject that nobody knows anything about that we can all talk about!” ― Richard Feynman
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment

#5 2012-11-06 01:40:53

Agnishom
Real Member
Award: Wink Sherlock

Offline

Re: Those inequalities again

Yes! smile 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'
'Who are you to judge everything?' -Alokananda

#6 2012-11-06 01:43:35

anonimnystefy
Real Member

Online

Re: Those inequalities again

You are welcome!


The limit operator is just an excuse for doing something you know you can't.
“It's the subject that nobody knows anything about that we can all talk about!” ― Richard Feynman
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment

Board footer

Powered by FluxBB