【C++】 求方程ax^2+bx+c=0的根,用3个函数分别求答:include <iostream>#include <cmath>using namespace std;double f1(double,double,double);//声明和定义不相符double f2(double,double,double);double f3(double,double,double);int main(){ double a,b,c,x1,x2; cin>>a>>b>>c; f1(a,b,c); f2(a,b,c); f3(a,b,...