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## #1 2013-10-27 16:52:26

niharika_kumar
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### triangles and circles

Q.ABC is a triangle, right angled at B. A circle is inscribed in it.The lengths of the 2 sides containing the r8 angle are 6 nd 8 cm
Find the radius of the circle.

*You are never as good as people tell you when you win and you are never as bad as they tell you when you lose.

*Everything happens for a reason,even if we are not wise enough to see them....oprah winfrey

## #2 2013-10-27 20:16:38

bob bundy
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### Re: triangles and circles

hi niharika_kumar

Diagram below.  I've labelled the points where the triangle touches the circle D, E and F and the centre O.

I've then done a similar x, y, z trick, like I did for your previous question.

Note.  OFB = 90  as AB is a tangent, ODB = 90 as BC is a tangent and ABC = 90 was given.

So OFBD is a square.  => once we know 'y', we also know the radius.

Method:

(i) Work out AC using Pythagoras.

(ii) Make equations for x + y, for x + z, and for y + z.

(iii) Find x, y, and z.

Let me know when you get an answer and I'll check it for you.

Bob

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

## #3 2013-10-27 22:41:21

bob bundy
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### Re: triangles and circles

hi bobbym,

Angle bisectors.

Bob

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

## #4 2013-10-27 22:59:46

bobbym

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### Re: triangles and circles

Hi Bob;

In mathematics, you don't understand things. You just get used to them.
Some cause happiness wherever they go; others, whenever they go.
If you can not overcome with talent...overcome with effort.

## #5 2013-10-27 23:10:20

bob bundy
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### Re: triangles and circles

hi bobbym,

Bob

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

## #6 2013-10-27 23:16:19

bobbym

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### Re: triangles and circles

Hi bob;

I agree with your angle bisector idea. At present, I do not know how that formula was derived.

In mathematics, you don't understand things. You just get used to them.
Some cause happiness wherever they go; others, whenever they go.
If you can not overcome with talent...overcome with effort.

## #7 2013-10-27 23:16:37

bob bundy
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### Re: triangles and circles

hi bobbym,

edit:  I think I have a book with it in but it's just been put back in the loft.

Bob

Last edited by bob bundy (2013-10-27 23:18:13)

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

## #8 2013-10-27 23:28:07

bobbym

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### Re: triangles and circles

Hi bob;

Check this page out. This point of intersection is called the incenter.

http://en.wikipedia.org/wiki/Incenter

In mathematics, you don't understand things. You just get used to them.
Some cause happiness wherever they go; others, whenever they go.
If you can not overcome with talent...overcome with effort.

## #9 2013-10-27 23:47:09

Agnishom
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### Re: triangles and circles

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'
'The whole person changes, why can't a habit?' -Alokananda

## #10 2013-10-28 00:04:40

bob bundy
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### Re: triangles and circles

Why?

#### Bob Bundy wrote:

Note.  OFB = 90  as AB is a tangent, ODB = 90 as BC is a tangent and ABC = 90 was given.

So OFBD is a square.  => once we know 'y', we also know the radius.

B

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

## #11 2013-10-28 02:41:27

bob bundy
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### Re: triangles and circles

hi bobbym,

#### You wrote:

Arhh yes.  I thought it had shades of Heron's formula in it.  My book has the proof for Heron, so that sews it up nicely.  Thanks.

Bob

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

## #12 2013-10-28 02:51:53

Agnishom
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### Re: triangles and circles

'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'
'The whole person changes, why can't a habit?' -Alokananda

## #13 2013-10-28 03:13:48

bobbym

Online

### Re: triangles and circles

Hi;

In mathematics, you don't understand things. You just get used to them.
Some cause happiness wherever they go; others, whenever they go.
If you can not overcome with talent...overcome with effort.

## #14 2013-10-28 03:19:48

Agnishom
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### Re: triangles and circles

The person above can explain post 3

'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'
'The whole person changes, why can't a habit?' -Alokananda

## #15 2013-10-28 03:23:32

bobbym

Online

### Re: triangles and circles

Yes, there was a geogebra post I was working on. When I got to the end of it, it did not work. That is bob's improvement which I used in the new post.

In mathematics, you don't understand things. You just get used to them.
Some cause happiness wherever they go; others, whenever they go.
If you can not overcome with talent...overcome with effort.

## #16 2013-10-28 03:43:35

Agnishom
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### Re: triangles and circles

So, there is a deleted post?

'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'
'The whole person changes, why can't a habit?' -Alokananda

## #17 2013-10-28 04:58:09

bobbym

Online

### Re: triangles and circles

You can say it is an overwritten post.

In mathematics, you don't understand things. You just get used to them.
Some cause happiness wherever they go; others, whenever they go.
If you can not overcome with talent...overcome with effort.

## #18 2013-10-28 23:48:23

Agnishom
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### Re: triangles and circles

Did you know  that 'Niharika' means Nebula?

'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'
'The whole person changes, why can't a habit?' -Alokananda

## #19 2013-10-29 01:03:33

bobbym

Online

### Re: triangles and circles

I did not know that. But how would I?

In mathematics, you don't understand things. You just get used to them.
Some cause happiness wherever they go; others, whenever they go.
If you can not overcome with talent...overcome with effort.

## #20 2013-10-29 23:07:52

niharika_kumar
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### Re: triangles and circles

wow ,such a long thread following my ques.
@bob i found the ans. as radius= 2cm. thnx for your help.
@agnishom yes its meaning is nebula
@bobbym thnx

*You are never as good as people tell you when you win and you are never as bad as they tell you when you lose.

*Everything happens for a reason,even if we are not wise enough to see them....oprah winfrey

## #21 2013-10-29 23:32:41

Agnishom
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### Re: triangles and circles

#### bobbym wrote:

But how would I?

@Niharika, I know. I am bengali too.

'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'
'The whole person changes, why can't a habit?' -Alokananda

## #22 2013-10-29 23:54:54

bob bundy
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### Re: triangles and circles

hi niharika_kumar

Yes, your question certainly sparked some interest.  And 2 cm is the answer everyone got.

Bob

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

## #23 2013-10-30 03:27:18

niharika_kumar
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### Re: triangles and circles

@agnishom, well but i am not a bengali!

*You are never as good as people tell you when you win and you are never as bad as they tell you when you lose.

*Everything happens for a reason,even if we are not wise enough to see them....oprah winfrey