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On 5/20/2009 7:20 PM snipped-for-privacy@verizon.net spake thus:

Like more than half the respondents to this thread, you completely missed the point.

I know how to do that. I wasn't asking for a demonstration; I was asking for a***proof***.

(Even though your description contains some of the elements of a proof.)

spake thus:

State the axioms you wish to start with, and we'll take it from there. I'm sure someone here knows how to write a proof. A calculation based explanation is a good proof if one axiomizes high school geometry. This seems like the right approach here in rec.woodworking!

It seems to be based on calculation (360/6), but obscures that fact; I would expect better work from a math major.

LOL!

Obviously, as your previous post hinted, the OP didn't really want a formal proof. (He may not realize that is not what he wanted, but the fact that this question was raised because of not having an old geometry text is a pretty good clue.) What he wanted was a logical demonstration based on facts he accepted, with steps he didn't have to figure out. Note the range of logically identical responses here that have been dismissed as "mere demonstrations" or accepted as "proofs" depending on the number and detail of the steps explicitly stated, and whether the steps were numbered and labeled "proof" <g>.

Reminds me of a quote from a physics professor.

"You want an easy proof for the law of gravity? Step out of the window."

Your LOL is well taken. I'm not sure whether one needs the numbers in between the fractions (like sqrt(2)) for woodworking, nor any negative numbers, imaginary numbers, non-real complex numbers, nor probably any numbers bigger than 500. Maybe that's why those aren't marked on the ruler. :)

Bill

Do you think 1 53/128 would suffice (somebody with good eyesight might be able to mark it off a ruler with 64th's). I'd do better with a micrometer. I hope the wood is very stable. :)

Similarly, 1/2/sqrt(3) are the sides of a 30/60/90 triangle.

Interesting projects! My wife is supportive of amost any outlay for tools as long as I build her some "bird-related" stuff (feeders, houses, etc). Birds don't tend to be particular beyond a 16th of an inch. :)

Bill

#### Site Timeline

- posted on May 21, 2009, 4:13 am

Like more than half the respondents to this thread, you completely missed the point.

I know how to do that. I wasn't asking for a demonstration; I was asking for a

(Even though your description contains some of the elements of a proof.)

--

Found--the gene that causes belief in genetic determinism

Found--the gene that causes belief in genetic determinism

- posted on May 21, 2009, 9:33 am

State the axioms you wish to start with, and we'll take it from there. I'm sure someone here knows how to write a proof. A calculation based explanation is a good proof if one axiomizes high school geometry. This seems like the right approach here in rec.woodworking!

- posted on May 21, 2009, 4:25 pm

spake thus:

sides

asking

proof.)

See: http://www.nvcc.edu/home/tstreilein/constructions/Inscribed/inscribe4.htm

for the proof.

Len

sides

asking

proof.)

See: http://www.nvcc.edu/home/tstreilein/constructions/Inscribed/inscribe4.htm

for the proof.

Len

- posted on May 21, 2009, 6:04 pm

On 5/21/2009 9:25 AM Len spake thus:

Thank you. That was exactly what I was looking for.

There; was that so hard?

Thank you. That was exactly what I was looking for.

There; was that so hard?

--

Found--the gene that causes belief in genetic determinism

Found--the gene that causes belief in genetic determinism

- posted on May 21, 2009, 7:07 pm

"David Nebenzahl" wrote:

Same proof I gave you almost a week ago.

Lew

Same proof I gave you almost a week ago.

Lew

- posted on May 21, 2009, 7:47 pm

It seems to be based on calculation (360/6), but obscures that fact; I would expect better work from a math major.

- posted on May 21, 2009, 8:25 pm

LOL!

Obviously, as your previous post hinted, the OP didn't really want a formal proof. (He may not realize that is not what he wanted, but the fact that this question was raised because of not having an old geometry text is a pretty good clue.) What he wanted was a logical demonstration based on facts he accepted, with steps he didn't have to figure out. Note the range of logically identical responses here that have been dismissed as "mere demonstrations" or accepted as "proofs" depending on the number and detail of the steps explicitly stated, and whether the steps were numbered and labeled "proof" <g>.

--

Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

- posted on May 21, 2009, 8:31 pm

Reminds me of a quote from a physics professor.

"You want an easy proof for the law of gravity? Step out of the window."

--

-MIKE-

"Playing is not something I do at night, it's my function in life"

-MIKE-

"Playing is not something I do at night, it's my function in life"

Click to see the full signature.

- posted on May 21, 2009, 8:40 pm

-MIKE- wrote:

Obviously, that proof makes the assumption that the classroom in question is in an inertial reference frame. :)

Chris

Obviously, that proof makes the assumption that the classroom in question is in an inertial reference frame. :)

Chris

- posted on May 21, 2009, 9:18 pm

Chris Friesen wrote:

The window was in a big frame, on the 5th floor. :-)

The window was in a big frame, on the 5th floor. :-)

--

-MIKE-

"Playing is not something I do at night, it's my function in life"

-MIKE-

"Playing is not something I do at night, it's my function in life"

Click to see the full signature.

- posted on May 21, 2009, 9:31 pm

Your LOL is well taken. I'm not sure whether one needs the numbers in between the fractions (like sqrt(2)) for woodworking, nor any negative numbers, imaginary numbers, non-real complex numbers, nor probably any numbers bigger than 500. Maybe that's why those aren't marked on the ruler. :)

Bill

- posted on May 21, 2009, 10:02 pm

Bill wrote:

sqrt(2) is useful to find the length of the long side of a 45/45/90 triangle. Similarly, 1/2/sqrt(3) are the sides of a 30/60/90 triangle.

Numbers bigger than 500 are useful when working in millimetres.

I'm up in Canada and I know a guy who does everything in mm. Although the initial conversion of regular North American lumber dimensions to mm is a bit of a pain, it makes subsequent math a lot simpler. And of course all the Euro stuff just works...

Chris

sqrt(2) is useful to find the length of the long side of a 45/45/90 triangle. Similarly, 1/2/sqrt(3) are the sides of a 30/60/90 triangle.

Numbers bigger than 500 are useful when working in millimetres.

I'm up in Canada and I know a guy who does everything in mm. Although the initial conversion of regular North American lumber dimensions to mm is a bit of a pain, it makes subsequent math a lot simpler. And of course all the Euro stuff just works...

Chris

- posted on May 21, 2009, 10:12 pm

Do you think 1 53/128 would suffice (somebody with good eyesight might be able to mark it off a ruler with 64th's). I'd do better with a micrometer. I hope the wood is very stable. :)

Similarly, 1/2/sqrt(3) are the sides of a 30/60/90 triangle.

- posted on May 21, 2009, 10:42 pm

Bill wrote:

It might depend on what you're doing. The ribs at

http://www.iedu.com/DeSoto/Projects/Stirling/Heat.html

needed to be cut so that the length along the parabola was exactly four feet (the mirror width) and with accuracy to provide a good optical focus along the entire eight-foot length - and...

...the tenoned parts shown at the bottom of

http://www.iedu.com/DeSoto/Projects/Bevel /

were for silverware trays with diagonal dividers; these were the divider blanks, and they needed to* /exactly/ *fit (on* /both/ *ends :) ).

And no, none of the numbers needed were marked on any of my rulers. :)

It might depend on what you're doing. The ribs at

http://www.iedu.com/DeSoto/Projects/Stirling/Heat.html

needed to be cut so that the length along the parabola was exactly four feet (the mirror width) and with accuracy to provide a good optical focus along the entire eight-foot length - and...

...the tenoned parts shown at the bottom of

http://www.iedu.com/DeSoto/Projects/Bevel /

were for silverware trays with diagonal dividers; these were the divider blanks, and they needed to

And no, none of the numbers needed were marked on any of my rulers. :)

--

Morris Dovey

DeSoto Solar

Morris Dovey

DeSoto Solar

Click to see the full signature.

- posted on May 21, 2009, 10:58 pm

Interesting projects! My wife is supportive of amost any outlay for tools as long as I build her some "bird-related" stuff (feeders, houses, etc). Birds don't tend to be particular beyond a 16th of an inch. :)

Bill

- posted on May 21, 2009, 11:25 pm

Morris Dovey wrote:

Am I the only one would rather mark than measure?

Like if I have a piece of trim that needs to fit between A and B, I don't measure A to B then measure that out on the trim. I hold up the trim between A and B and mark the trim.

Am I the only one would rather mark than measure?

Like if I have a piece of trim that needs to fit between A and B, I don't measure A to B then measure that out on the trim. I hold up the trim between A and B and mark the trim.

--

-MIKE-

"Playing is not something I do at night, it's my function in life"

-MIKE-

"Playing is not something I do at night, it's my function in life"

Click to see the full signature.

- posted on May 21, 2009, 11:30 pm

-MIKE- wrote:

Before some smarta$$ says, what do you do with a 12' piece of crown molding.... I obviously call a couple friends to come over and hold it in place for me. duh.

Before some smarta$$ says, what do you do with a 12' piece of crown molding.... I obviously call a couple friends to come over and hold it in place for me. duh.

--

-MIKE-

"Playing is not something I do at night, it's my function in life"

-MIKE-

"Playing is not something I do at night, it's my function in life"

Click to see the full signature.

- posted on May 21, 2009, 11:42 pm

-MIKE- wrote:

What do you do with a 12' piece of crown molding on an outside corner that isn't square?

Chris

What do you do with a 12' piece of crown molding on an outside corner that isn't square?

Chris

- posted on May 22, 2009, 1:47 am

Chris Friesen wrote:

I can't tell is I "wooshed" you or you, me. :-)

I can't tell is I "wooshed" you or you, me. :-)

--

-MIKE-

"Playing is not something I do at night, it's my function in life"

-MIKE-

"Playing is not something I do at night, it's my function in life"

Click to see the full signature.

- posted on May 21, 2009, 11:52 pm

-MIKE- wrote:

If it'll help you feel better, I neither marked* /nor/ *measured for those
projects - everything was cut from unmarked stock and then assembled as cut.

I did have drawings for the silverware trays because the customer needed something to sign off on, but the drawings for the parabolic trough came along after the fact, to document what had been done.

For stuff I don't need to be fussy about, I've had to switch to a light touch with a knife - my eyes just aren't good enough any longer to split a pencil mark...

If it'll help you feel better, I neither marked

I did have drawings for the silverware trays because the customer needed something to sign off on, but the drawings for the parabolic trough came along after the fact, to document what had been done.

For stuff I don't need to be fussy about, I've had to switch to a light touch with a knife - my eyes just aren't good enough any longer to split a pencil mark...

--

Morris Dovey

DeSoto Solar

Morris Dovey

DeSoto Solar

Click to see the full signature.

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