#include <iostream>
#include <cmath>
using namespace std;

int main() {
	double x, eps;
	double F=x, a=x;
	int n=0;
	cout << "Введите значение аргумента и точности:" << endl;
	cin >> x >> eps;

	while (fabs(a)<=eps)
	{
		a*=х*х/(n*2+1);
		F+=a;
		n++;

	}
	cout << "Приближенное значение arcth X=" << F;
	cout << "Точное значение arcth X=" << atanh(x) << endl; //atanh(x) = 1/2*((1+x)/(1-x))
	return 0;
}

15:06:54 **** Incremental Build of configuration Debug for project Lr3 ****
make all
Building file: ../src/Lr3.cpp
Invoking: Cross G++ Compiler
g++ -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"src/Lr3.d" -MT"src/Lr3.d" -o "src/Lr3.o" "../src/Lr3.cpp"
../src/Lr3.cpp:22:3: error: stray ‘\321’ in program
   a*=х*х/(n*2+1);
   ^
../src/Lr3.cpp:22:3: error: stray ‘\205’ in program
../src/Lr3.cpp:22:3: error: stray ‘\321’ in program
../src/Lr3.cpp:22:3: error: stray ‘\205’ in program
../src/Lr3.cpp: In function ‘int main()’:
../src/Lr3.cpp:22:11: error: expected primary-expression before ‘/’ token
   a*=х*х/(n*2+1);
           ^
make: *** [src/Lr3.o] Ошибка 1