private double calcDerivative(double point) {
        double value = 0;
        for (int  i = 0; i < equationCoef.length; i++) {
            if (equationPower[i] != 0) {
                if (equationPower[i] == 1) {
                    value = value + equationCoef[i]; 
                } else {
                    value = value + equationCoef[i] * equationPower[i] * Math.pow(point, equationPower[i] - 1);
                }
            }
        }
        return value;
    }