math help

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I need to build a octagon, outside diameter of 12 inch. I know the cut will be 22.5 but what is the length? I know how to do this, but for the life of me I am drawing a blank this morning.

I am getting 4.97 inch, guess I should throw that out as well. Sound right?
 
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I'm drawing a blank too, but I want to say you're looking for the hypotenuse of an acute triange (one which all angles are less than 90 degrees). Haven't found a good example of the forumla or a calculator. :huh: All calculators I've found for hypotenuse are based on one side being 90 degrees.
 
No lets see it been 40 years since I had to do this but as I recall This is a SAS problem. Side Angle Side. You take the length of the two side squared and add them together multiply the by the sine of the included angle and take the square root of the result.
 
I need to build a octagon, outside diameter of 12 inch. I know the cut will be 22.5 but what is the length? I know how to do this, but for the life of me I am drawing a blank this morning.

I am getting 4.97 inch, guess I should throw that out as well. Sound right?

Steve,

You need to clarify whether the diameter is to the corners or flats. The length of a side for 12" dia. to corners is 4 19/32. The length of a side for 12" dia. to flats is 4 31/32 (4.971). I didn't calculate this. I cheated and used CADD.;)

Ike ( Retired Drafting Teacher)
 
Edge length = Diameter x sin(180/#sides) for flat to flat (i.e. circle fits inside regular polygon)

Edge length = Diameter x tan(180/#sides) for corner to corner (i.e. regular polygon fits inside circle)
 
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