1.30.rkt

#lang sicp

(define (sum-linear-recursion term a next b) 
   (if (> a b) 
       0 
       (+ (term a) 
          (sum term (next a) next b))))

(define (sum term a next b) 
   (define (iter a result)
     (if (> a b)
         result
         (iter (next a) (+ result (term a)))))
   (iter a 0))