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HW4 #2
standarddeviation.rkt by Ryan Liszewski
Calculates the standard deviation sigma from the given number(s)
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#lang racket
(define (squarenumber x)
  (* x x))

(define (listsum lst)
  (if (null? lst) 0
      (+ (car lst) (listsum (cdr lst)))))

(define (squarelist lst)
  (if (null? lst) 0
      (+ (squarenumber (car lst)) (squarelist (cdr lst)))))

(define sigma (lambda x(sqrt (- (/ (squarelist x) (length x))
                                 (squarenumber (/ (listsum x) (length x)))))))