# Find arc radius given length and chord

• 2010-02-10, 03:12 PM
jodi_sherrell
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.
• 2010-02-10, 04:05 PM
buzz
Re: Find arc radius given length and chord
```;;; 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)             "\nRadius = " (rtos rad)             "\nAngle = " (angtos ang) )   )   (princ) )```