?? 用截弦法求方程的根.cpp
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/*用截弦法求方程的根*/
#include<stdio.h>
#include<math.h>
float f(float );
float xpoint(float ,float );
float root(float ,float );
void main()
{
float x1,x2,f1,f2,x;
do
{
printf("input x1,x2:\n");
scanf("%f%f",&x1,&x2);
f1=f(x1);
f2=f(x2);
}
while (f1*f2>=0);
x=root(x1,x2);
printf("A root of equation is %7.2f",x);
}
float f(float x)
{
return ((x-5.0)*x+16.0 )*x-80.0;
}
float xpoint(float x1,float x2)
{
return (x1*f(x2)-x2*f(x1))/( f(x2)-f(x1) );
}
float root(float x1,float x2)
{
int i;float x,y,y1;
y1=f(x1);
do
{
x=xpoint(x1,x2);
y=f(x );
if(y*y1>0)
{
y1=y;x1=x;
}
else
x2=x;
}
while(fabs(y )>=0.0001);
return(x);
}
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