sicp每日一题[1.40]

Exercise 1.40

Define a procedure cubic that can be used together with the newtons-method procedure in expressions of the form

(newtons-method (cubic a b c) 1)

to approximate zeros of the cubic $x^3 + ax^2 + bx + c$.

这道题很简单，把 (cubic a b c) 实现就行了。

(define (cubic a b c)
  (lambda (x) (+ (cube x)
                 (* a (square x))
                 (* b x)
                 c)))

; 求 x^3 + x^2 + x + 1 = 0 的解
(newtons-method (cubic 1 1 1) 1)

; 答案：-1.000000022096024，也就是 -1