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## #1 2013-11-17 16:48:17

shivusuja
Member
Registered: 2006-09-14
Posts: 56

### Triangles

Please Help Me Out

Sum Of The Altitudes Of Triangle Is Less Than He The Sum Of The Sides Of The Triangle.
(ae+cf+bd < Ab+bc+cd)

Proof
I Have Tried With
Sum Of The Two Sides Is Greater Than The Third Side
Abc As Sides Of The Triangle And Ae. Bd And Cf As The Altitude.
I Got

Ae+ec>ac      Bd+dc>bc   Cf+af>ac
Ae+be>ab      Bd+ad>ab   Cf+fb>bc

Adding All I Got 2ae+2bd+2cf>ab+bc+ca

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## #2 2013-11-18 01:02:55

bob bundy
Moderator
Registered: 2010-06-20
Posts: 7,766

### Re: Triangles

hi shivusuja

I spent ages working around the triangle inequality and got nowhere.  Then I had a fresh idea.

AEC is a right angled triangle with AC as hypotenuse.  So

AE < AC

Similarly, in triangle CFB

CF < BC

And finally, in triangle ABD

BD < AB

Add those up and

AE + CF + BD < AC + BC + AB

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

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## #3 2013-11-18 01:40:27

Agnishom
Real Member
From: Riemann Sphere
Registered: 2011-01-29
Posts: 24,583
Website

### Re: Triangles

Thank You, Bob

'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 2013-11-18 16:12:55

shivusuja
Member
Registered: 2006-09-14
Posts: 56

### Re: Triangles

THANKS
SO SIMPLE WHOLE DAY I WORKED OUT. THIS IS 5 MARKS QUESTION. DO I GET 5 MARKS IF I DO IN THIS WAY?

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## #5 2013-11-18 16:26:08

Agnishom
Real Member
From: Riemann Sphere
Registered: 2011-01-29
Posts: 24,583
Website

### Re: Triangles

Yes, atleast in CBSE

'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 2013-11-18 21:01:48

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,018

### Re: Triangles

The harder question is, can you prove the same thing, but with medians instead of heights?

Last edited by anonimnystefy (2013-11-18 21:02:10)

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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## #7 2013-11-20 01:03:07

Agnishom
Real Member
From: Riemann Sphere
Registered: 2011-01-29
Posts: 24,583
Website

### Re: Triangles

anonimnystefy wrote:

The harder question is, can you prove the same thing, but with medians instead of heights?

A similar question came in my test and I could not answer

'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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