sicp 练习1.7

(define (mysqrt x)

    (sqrt-iter 1.0 x)) 

(define (sqrt-iter guess x)
     (if (good-enough? guess x)
         guess
         (sqrt-iter (improve guess x)
                     x)))

(define (good-enough? guess x)
     (<(/ (abs(- (improve guess x) guess)) guess) 0.00000000000000000000000000001))  //0多几个也没事，对这个困惑，精度是怎么处理的？

(define (improve guess x)

   (average guess (/ x guess))) 

           (define (average x y)  

               (/ (+ x y) 2))

          (define (square guess)
              (* guess guess ))

运行结果

> (mysqrt 2)
1.414213562373095（15位精度，而上面0.0000000…1那么多位都没事，困惑）
>