编写函数用以求表达式x的平方-5x+4的值,x作为参数传送给函数.调用此函数求：(后面的请看补充)

数学不好，折腾了好一会
#include
#include
double sum1(double x)
{double y1;
y1=(x-1)*(x-4);
return y1;
}
double sum2(double x)
{double y2;
y2=(x+15-1)*(x+15-4);
return y2;
}
double sum3(double x)
{double y3;
y3=(sin(x)-1)*(sin(x)-4);
return y3;
}
main()
{double x,y1,y2,y3;
printf(" y1=x^2-5x+4 \n y2=(x+15)^2-5(x+15)+4 \n y3=sin^2x-5sinx+4 \n请输入x求y1、y2、y3的值:");
scanf("%lf",&x);
printf("解: \n y1=%lf \n y2=%lf \n y3=%lf \n",sum1(x),sum2(x),sum3(x));
getch();
}

#include
#include
double f(double);
main()
{double x,y,y1,y2;
printf("请输入x\n");
scanf("%lf",&x);
y=2;y1=15+x;y2=sin(x);
printf("%lf %lf %lf",f(y),f(y1),f(y2));
}
double f(double a)
{double s;
s=(a*a-5*a+4);
return s;
}

#include
#include
double fun ( double x )
{ return (x*x-5*x+4); }
void main ()
{ double x,x1,x2,x3,y1,y2,y3;
printf ("Please input x:\n");
scanf ("%lf",&x);
x1=2; x2=x+15; x3=sin(x);
printf ("%lf\n%lf\n%lf\n",y1=fun(x1),y2=fun(x2),y3=fun(x3));
}

#include

float fun2(flaot x){
float y;
y=2*2-5*2+4;
return y;}

float fun2(flaot x){
float y;
y=(x+15)*(x+15)-5*(x+15)+4;
return y;}

float fun3(flaot x){
float y;
y=sin(x-5)*sin(x-5)*sin(x)+4;
return y;}