这里怎么了？错误为“[error]在数值常量之前应为‘，’或‘；’”

#include <iostream>
#include <cmath>
using namespace std;
int main()
{   
    double a = 8;
    double b = 2;
    double c = sqrt 8.0,2.0);
    cout << "a = 8\nb = 2\nc = square from 8 = " << c << "\n";
}