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Maths question...

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jbullfrog:

--- Quote from: Dustin Mustangs on June 12, 2006, 03:24:49 pm ---
--- Quote from: jbullfrog on June 12, 2006, 01:02:56 pm ---The formula that was given assumes that you're starting your cut at a 90 degree angle (perpendicular) to the top edge (should the top edge have been parallel to the ground)...
--- End quote ---

Just to set the record straight, the formula linked has nothing to do with anything surrounding the circle (or radius), just the circle itself.  The cut coming into or going out of the desired radius has no effect on the radius itself or the formula used to calculate it, so what was quoted above is incorrect.

Oh, and that's quite an interesting approach you have there Quarters...

--- End quote ---

Sorry for any confusion I might be causing, but what I'm describing is a concern...  although a fairly small one...

Hopefully the attached picture will help my explanation... 'h' and 'c/2' are given as they would need to be for the equation in question.  The problem is that the derivation of the equation relies on 'h' being a part of the radius of the circle while a radius will intersect the circle's circumference at a right angle.  This would mean that the angle 'A' shown in the attached picture would have to be a right angle which it is not (even very near where 'h' and the circumference intersect).  Given that 'A' is not a right angle, the equation would lead to an incorrect value for 'r'.

as stated before, to get an angle of 'A' that is a bit less than 90 degrees, increase whatever 'r' the equation gives you by a little bit and you should be good.

then again, maybe I'm not "looking at the same picture" you guys are:  maybe you guys are using a different 'c' and 'h' and I'm just confused  :P

I would also use the flexible ruler idea... you'd just be using a big protractor then ;)

holdennut:
Thanks for your concern jbullfrog but "h" in the equation isn't the radius. "h" is actually the height of the chord which is given as "c". (the picture in the link done in ASCII is a little confusing)

Dustin Mustangs:
Not to mention that assuming line 'h', as drawn by bullfrog, goes through the center point of the circle (which if it doesn't I have no idea what it would be useful for), angle 'A' will always be the same for any given circle so worrying about what 'A' is really doesn't make any sense.

jbullfrog:

--- Quote from: holdennut on June 13, 2006, 04:23:53 am ---Thanks for your concern jbullfrog but "h" in the equation isn't the radius. "h" is actually the height of the chord which is given as "c". (the picture in the link done in ASCII is a little confusing)

--- End quote ---

Yes, 'h' is the height of the chord, I understand that perfectly well... and because 'h' is the height of the chord, it goes through the center of the circle, as Dustin Mustangs points out (making it part of a line that describes a radius).  Also, just as Dustin Mustangs points out, any line that goes through the center of the circle will make the same angle with the circumference of the circle as any other line that goes through the center of the circle...  no matter what circle you are describing...

This angle will be a right angle.

really guys, go ahead and use the formula...  the radius it gives won't be that far off because the angle 'A' in the picture I linked to before is very close to 90 degrees...

have fun.

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