c语言-截弦法

//截弦法求方程 x^3-5*x^2+16x-80 = 0 在区间(-3,6)的根
#include <stdio.h>
#include <math.h>

//y=x^3-5*x^2+16x-80
double getY(double x) {
	return  pow(x, 3) - 5 * x * x + 16 * x - 80;
}
//两点确定一条直线, 直线在y=0时x的值
double getX(double x1, double x2) {
	return (x1 * getY(x2) - x2 * getY(x1)) / (getY(x2) - getY(x1));
}
void c(double x1, double x2) {
	double x3 = getX(x1, x2);
	printf("x1:%f y1:%f   x2:%f y2:%f   x3:%f y3:%f\n", x1, getY(x1), x2, getY(x2), x3, getY(x3));
	//递归,使得y接近0
	if (fabs(getY(x3)) > 0.00001) {
		if (getY(x1) * getY(x3) < 0) {
			c(x1, x3);
		}
		else {
			c(x3, x2);
		}
	}
	else {
		printf("result: %f", x3);
	}
}

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