#| BEGIN (Write your solution here) |#
(define (square-root x)
  (square-helper 0.1 x))

(define (square-helper guess x)
  (let ((pre-guess (improve guess x)))
      (if (good-enough? guess pre-guess)
          guess
          (square-helper pre-guess x))))

(define (improve guess x)
  (avg guess (/ x guess)))

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

(define (good-enough? guess pre-guess)
    (< (abs (- guess pre-guess)) 0.000000001))
#| END |#