Computing cubic polynomial

Question

I need a procedure that returns the value of a cubic polynomial, ie :

f(x) = x³ + ax² + bx + c

I should be able to do this with a procedure that takes three arguments and Newton-Raphson's method but I am at a loss on how.

(define f (cubic a b c) ...)

How can I do this?

Please note that "Questions asking for code must demonstrate a minimal understanding of the problem being solved. Include attempted solutions, why they didn't work, and the expected results." What have you tried so far? What didn't work about it? — Joshua Taylor, Oct 10 '13 at 13:22
Newtown's method is useful for (but not guarnteed) to find roots of a function. Finding the value at any particular x is a different beast. — WorBlux, Oct 10 '13 at 15:41
You have misunderstood either the problem or the solution. There's no point in trying to use Newton-Raphson to compute the *value* of a polynomial for a given input. — molbdnilo, Oct 11 '13 at 12:12

score 2 · Answer 1 · answered Oct 10 '13 at 13:21

Well you want your function to return a function so

(define cubic
   (lambda (a b c) ;; lambda #1
      (lambda (x) ;; lambda #2
        ???))) ;; x^3 a * x^2 + b * x + c

This is called a closure, lambda 2 is returned when lambda 1 is called and can remember and access the parameters from lambda #1's call.

Then

(define f (cubic a b c))

defines f to be a function taking in x and plugging it into lambda #2's body.

1 Answers1