;; (geo-seq beg len q) returns a (listof Num) that contains a geometric sequence
;;    whose first value is beg with a common ratio q and length len
;; geo-seq : Num Num Num -> (listof Num)
;; Example :
(check-expect (geo-seq 2 4 3) (list 2 6 18 54))

(define (geo-seq beg len q)
  (map (lambda (x) (* beg (expt q x))) (range 0 len 1)))

;; Tests :
(check-expect (geo-seq 3 3 2) (list 3 6 12))
(check-expect (geo-seq 4 5 -1) (list 4 -4 4 -4 4))