Q2.1-PRF192-PE-trial

double fen(double x, double epsi) {
    double si,a; int n;
    si = x; n = 1; a = x;
    while (epsi < fabs(a)) {
        a *= (-1) * pow(x,2) / (2*n*(2*n+1));
        si += a;
        n++;
    }
    return (si);
}