(define (sqrt2 n d)
(sqrt2-help n d 1 0))
(define (sqrt2-help n d guess prevguess)
(if (< (diff guess prevguess) (* d prevguess))
guess
(sqrt2-help n d (improve-guess n guess) guess)))
(define (diff a b)
(abs (- a b)))
(define (improve-guess n guess)
(average guess (/ n guess)))
(define (average a b)
(/ (+ a b) 2))