sicp 2.1

sicp_2_1

(define (make-rat n d)
  (if (> d 0)
  (cons n d) (cons (* -1 n) (* -1 d))
  
  ))

(define (numer x) (car x))
(define (denom x) (cdr x))

(define (mul-rat x y)
(make-rat 
      (* (numer x) (numer y))
      (* (denom x) (denom y))))

(define x (make-rat 1 -2))
(define y (make-rat 1 2))

(mul-rat x y)