Added my solutions so far

ex-1-11.rkt

@@ -0,0 +1,43 @@
+#lang racket
+
+;; for n=100
+;; iterative version takes roughly 0.008 milliseconds.
+;; recursive version does not seem like it will finish any time soon.
+;; for n=50
+;; iterative version takes roughly 0.003 milliseconds in drracket
+;; recursive version has not yet finished executing after a couple minutes, and I got bored.
+;; for n=25.
+;; iterative version takes 0.002ms
+;; recursive version takes 46.5 ms
+;; yeah. that's big. okay. this shit's important.
+;; I wonder how it would be with memoization.
+
+
+(define-syntax-rule (meas form)
+  (let ([my-time (current-inexact-milliseconds)])
+    (let ([res form])
+      (- (current-inexact-milliseconds) my-time))))
+
+
+(define (recursive n)
+    (if (< n 3)
+        n
+        (+ (recursive (- n 1))
+           (* 2 (recursive (- n 2)))
+           (* 3 (recursive (- n 3))))))
+(define (iter a b c n)
+  (if (<= n 0)
+      c
+      (iter b c (+ c (* 2 b) (* 3 a)) (- n 1))))
+(define (iter-start n)
+  (iter 0 1 2 (- n 2)))
+
+(define (ex-1-11 n)
+  (let loop ((i n))
+    (if (< i 2)
+        #t
+        (if (= (recursive i) (iter-start i))
+            (loop (- i 1))
+            (begin 
+              (display "UNEQUAL!")
+              (displayln i))))))