(define pi 3.14159)

(define (cont-frac n d k)
    (define (iter i acc)
      (let ((acc (/ (n i) (+ (d i) acc)))
            (i (- i 1)))
        (if (> i 0)
            (iter i acc)
            acc)))
    (iter k 0))

(define (tan-cf x k)
  (cont-frac (lambda (i) (if (= i 1) x (- (* x x))))
             (lambda (i) (- (* 2 i) 1))
             k))