(define (fixed-point f first-guess) 
  (define (close-enough? v1 v2) 
    (< (abs (- v1 v2) tolerance)) 
    (define (try guess) 
      (display guess) 
      (newline) 
      (let ((next (f guess))) 
        (if (close-enough? guess next) 
            next 
            (try next)))) 
    (try first-guess))) 

Should be

(define (fixed-point f first-guess) 
  (define (close-enough? v1 v2) 
    (< (abs (- v1 v2)) tolerance)) ;; note the extra parenthesis here
    (define (try guess) 
      (display guess) 
      (newline) 
      (let ((next (f guess))) 
        (if (close-enough? guess next) 
            next 
            (try next)))) 
    (try first-guess)) ;; and one removed here.