7-8.c

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/*牛顿迭代法*/
#include<stdio.h>
#include<math.h>
float solut(float a,float b,float c,float d)
{
	float x=1,x0,f,f1;
	do
	{
		x0=x;
		f=((a*x0+b)+c)*x0+d;
		f1=(3*a*x0+2*b)*x0+c;
		x=x0-f/f1;
	}
	while(fabs(x-x0)>=0.00001);
	return (x);
}
main()
{
	float a,b,c,d;
	printf("\n Input a,b,c,d=\n");
	scanf("%f,%f,%f,%f",&a,&b,&c,&d);
	printf("Equation is %5.2fX^3+%5.2fX^2+%5.2fX+%5.2f=0",a,b,c,d);
	printf("\n x=%10.7f\n",solut(a,b,c,d));
}