error C2447: missing function header (old-style formal list?)麻烦各位

大家好！这个程序报错了，我检查了好几遍，不得要领，麻烦各位帮我看看是怎么回事，用的是vc++。#include<stdio.h>#include<math.h>double fun(double x);{return (x*x-5*x+4);}main(){double x,y1,y2,y3;scanf("%lf",&x);y1=fun(2);y2=fun(x+15);y3=fun(sin(x));printf("%lf,%lf,%lf\n",y1,y2,y3);}提示：error C2447: missing function header (old-style formal list?) 收起