Zadanie z funkcją kwadratową

package com.Talar;
import static java.lang.Math.*;

public class funkcjaKwadratowa {
    private double a;
    private double b;
    private double c;
    private double x1;
    private double x2;

    public funkcjaKwadratowa(double a, double b, double c){
        if(a==0) this.a = ((b+c)/2);
        else this.a = a;
        this.b = b;
        this.c = c;
    }

    public double obliczWartosc(double x){
        double y = 0;
        y = (this.a * pow(x,2)) + (this.b * x) + this.c;
        return y;
    }

    public int ilePierwiastkow(){
        int ilosc = 0;
        double delta = pow(this.b,2) - 4 * this.a * this.c;
        if(delta < 0) ilosc = 0;
        else if(delta == 0){
            ilosc = 1;
            this.x1 = (this.b/2*this.a) * -1;
        }
        else if(delta > 0){
            ilosc = 2;
            this.x1 = (((this.b*(-1))+sqrt(delta))/(2*this.a));
            this.x2 = (((this.b*(-1))-sqrt(delta))/(2*this.a));
        }

        return ilosc;
    }
}