Eval square root by Newton's method

[Scheme] square root

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

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

(define (my-abs x)
  (cond ((< x 0)(- x))
        ((= x 0) 0)
        ((> x 0) x)))

(define (my-sqrt x)
  (define (improve guess)
    (average guess (/ x guess)))
  (define (good-enough? guess)
    (< (my-abs (- (square guess) x))
    .001))
  (define (try guess)
    (if (good-enough? guess)
        guess
        (try (improve guess))))
  (try 1))

(display (my-sqrt 36))