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Answers for “为什么牛顿法需要可用的导数?”

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The mathematical iteration formula for Newton's method is xn+1=xn−f(xn)f′(xn)x_{n+1} = x_n - \frac{f(x_n)}{f'(x_n)}. This formula updates the current guess xnx_n to the next guess xn+1x_{n+1} by subtracting the ratio of the function value to its derivative.

Conditions: f′(xn)f'(x_n) must be available and nonzero for the displayed division.; The formula gives one iterative update from xnx_n to xn+1x_{n+1}.

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A major weakness of Newton's method is that it requires derivatives to be available for the function. If exact derivatives are unavailable, they can be estimated using finite differencing, but this can lead to slower and less reliable convergence.

Conditions: Newton's method requires derivative values at the iterates.; Finite differencing is offered as an estimation method, not as an equivalent guaranteed replacement.