연습문제 1.39

(define (tan-cf x k)
  (define (inner-tan i)
    (/
     (if (= i 1)
         x
         (square x))
     (- (- (* i 2) 1)
        (if (= i k)
            0
            (inner-tan (+ i 1))))))
  (inner-tan 1))