先表示delta再求解

#include <iostream>
#include <cstring>
#include <algorithm>
#include <cmath>

using namespace std;

double a, b, c, delta;
int main()
{
    cin >> a >> b >> c;
    delta = b * b - 4 * a * c;

    if (delta < 0 || a == 0) cout << "Impossivel calcular" << endl;
    else {
        printf("R1 = %.5lf\nR2 = %.5lf", ((-1) * b + sqrt(delta)) / (2 * a),((-1) * b - sqrt(delta)) / (2 * a));
    }

    return 0;
}