To determine real roots of quadratic equation

QuadraticEquationDemo.java

/**
 * Example to determine real roots of a Quadratic Equation
 * The Standard Form of a Quadratic Equation looks like this: ax2 + bx + c =0
 * d= b2 - 4ac
 * When b2 − 4ac is positive, we get two Real solutions. There are two real roots.
 * When it is zero we get just ONE real solution (both answers are the same). There is one real root.
 * When it is negative we get a pair of Complex solutions. There are no real roots.
 *
 * Reference: https://www.mathsisfun.com/quadratic-equation-solver.html
 * https://www.mathsisfun.com/algebra/quadratic-equation.html
 * http://www.biology.arizona.edu/biomath/tutorials/quadratic/roots.html
 * */
public class QuadraticEquationDemo {
    public static void main(String[] args) {
        double a, b, c, d;
        double x1,y1;
        a=1;
        b=-3;
        c=4;
        d = Math.pow(b,2) - 4*a*c;
        System.out.println("D is: " +  d);

        if(d>0){
            x1 = (-b + Math.sqrt(d))/(2*a);
            y1 = (-b - Math.sqrt(d))/(2*a);
            System.out.println("Roots of equation:" + x1 + "," + y1);
        }
        else if (d==0){
            x1= -b/(2*a);
            System.out.println("Only one root of equation is :" + x1);
        }
        else{
            System.out.println("No real roots");
        }

    }
}

###Sample Data
a=2;
b=5;
c=3;

Output:
D is: 1.0
Roots of equation:-1.0,-1.5

Sample Data:

a=-4;
b=12;
c=-9;

Output:
D is: 0.0
Only one root of equation is :1.5

Sample Data:

a=2;
b=-11;
c=5;

Output:
D is: 81.0
Roots of equation:5.0,0.5

Sample Data:

a=1;
b=-3;
c=4;

Output:
D is: -7.0
No real roots