建民打卡日记4.18

一、问题描述

二、设计思路

三、程序流程图

四、代码实现

#include <iostream>
#include <math.h>
using namespace std;

int main() {
	double newt(float a, float b, float c, float d);
	float a, b, c, d, x;
	cin >> a >> b >> c >> d;
	x = newt(a, b, c, d);
	printf("%lf", x);
}

double newt(float a, float b, float c, float d) {
	double x0, x = 1.5, f, fd, h;
	double k;
	while (x) {
		x0 = x;
		f = a * x0 * x0 * x0 + b * x0 * x0 + c * x0 + d;
		fd = 3 * a * x0 * x0 + 2 * b * x0  + c;
		h = f / fd;
		x = x0 - h;
		k = x - x0;
		if (k < 0)
			k *= -1;
		if (k <= 1e-5)
			break;
	}
	return x;
}