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## Find arc radius given length and chord

Does anyone know how to draw an arc when only given the arc length and chord length?

I know that the chord length is 19'-4 1/2" and I know that the arc length is 24'-8". How do I find the radius?

Any help would be greatly appreciated.  Reply With Quote

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## Re: Find arc radius given length and chord

-Buzz  Reply With Quote

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## Re: Find arc radius given length and chord

From the wizard known as _gile:

Code:
```;;; ArcChord->Angle (Newton method) by _gile
;;; Returns the arc angle according to its chord and length

(defun ArcChord->Angle (arc corde / k x)
(setq k (/ corde arc)
x (sqrt (- 6 (* 6 k)))
)
(repeat 6
(setq x (- x (/ (- (sin x) (* k x)) (- (cos x) k))))
)
(* 2 x)
)
;;;======================================;;;
;;;Testing command
(defun c:test (/ chord arc ang rad)
(while
(not
(and (setq chord (getdist "\nLength of chord: "))
(setq arc (getdist "\nLength of arc: "))
(< chord arc)
)
)
(prompt "Try again -- arc must be longer than chord.")
)

(setq ang (ArcChord->Angle arc chord)
rad (/ chord (* 2. (sin (/ ang 2.)))) )
(prompt
(strcat "\nChord length = " (rtos chord)
"\nArc length = " (rtos arc)  Reply With Quote