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 x³ + ax² + bx + c.

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

Or in Haskell:

cubic a b c x = x^3 + a*x^2 + b*x + c

(Which can be used the same way because of partial application.)