help please, why writes nan, and how to fix it?

Question

#include <iostream>
#include <math.h>
using namespace std;
const float a=2.05;
double p(double k)
{ double p1;
p1= (atan(k)+ (asin(a))/k);
return(p1);
}
int main()
{
double x,y,z,F;
cout<<"x="; cin>>x;
cout<<"y="; cin>>y;
cout<<"z="; cin>>z;
F= log10( p(x) + p(y)) - log( p(z));
cout<<"F="<<F<<endl;
return 0;
}

Answer 1

NaN stands for Not a Number, in this case for example if x, y or z =0 you get a division by 0 that has undefined behavior