用牛頓法求平方根
(define (average x y)
(/ (+ x y) 2)
)
(define (improve guess x)
(average guess (/ x guess))
)
(define (sqrt-iter guess x)
(if (good-enough? guess x)
guess
(sqrt-iter(improve guess x)
x
)
)
)
(define square x
(* x x)
)
(define (good-enough? guess x)
(< (abs (- (square guess) x ) 0.001 ))
)
(define (sqrt x)
(sqrt-iter 1.0 x)
)
