#lang sicp

(define (cont-frac n d k)
  (define (cf-acc n d k i)
    (if (= k i)
        (/ (n i) (d i))
        (/ (n i) (+ (d i) (cf-acc n d k (+ i 1))))))
  (cf-acc n d k 0))

(define (tan-cf x k)
  (cont-frac (lambda (i) (if (= i 0)
                             x
                             (- (* x x))))
             (lambda (i) (+ 1.0 (* 2.0 i)))
             k))