x1,x2都开根号，可以写到一起

(2*a)要加括号

#include<cstdio>
#include<iostream>
#include<cmath>
using namespace std;
int main()
{
    double a,b,c;
    cin>>a>>b>>c;
    double t=b*b-4*a*c;
    if(a==0||t<0) printf("Impossivel calcular\n");
    else
    {
        t=sqrt(t);
        double x1=(-b+t)/(2*a);
        double x2=(-b-t)/(2*a);
        printf("R1 = %.5lf\n",x1);
        printf("R2 = %.5lf\n",x2);
    }
    return 0;
}