(define (sqrt x)
  (sqrt-iter 1.0 (improve 1.0 x) x))

(define (sqrt-iter prev-guess next-guess x)
  (if (good-enough? prev-guess next-guess)
      next-guess
      (sqrt-iter next-guess (improve next-guess x) x)))

(define (improve guess x)
  (average guess (/ x guess)))

(define (average x y)
  (/ (+ x y) 2))

(define (good-enough? guess next-guess)
  (< (abs (- guess next-guess)) (* guess 0.00001)))

(define (square x)
  (* x x))