给定定义在【L，R]上的单调函数f（x），求方程的根

//给定定义在【L，R]上的单调函数f（x），求方程的根
const double eps=1e-5;
double f(double x){
    return ...;
}
double solve(double L,double R){
    double left=L,right=R,mid;
    while(right-left>eps){
        mid=(left+right)/2;
        if(f(mid)>0){
            right=mid;
        }else{
            left=mid;
        }
    }
    return mid;
}
//计算根号2
const double eps=1e-5;
double f(double x){
    return x*x;
}
double calSqrt(){
    double left=1,right=2,mid;
    while(right-left>eps){
        mid=(left+right)/2;
        if(f(mid)>2){
            right=mid;
        }else{
            left=mid;
        }
    }
    return mid;
}