quadratic equation

Question

public class Program
{
public static void main(String[] args) {
float a = 1.0f ;
float b = 2.0f ;
float c = -3.0f ;
float x =(float) (-b + Math.sqrt((b*b)-(4*a*c)))/(2*a);
System.out.println(x);
float y = (float) (-b - Math.sqrt((b*b)-(4*a*c)))/(2*a);
System.out.println(y);
}
}
QUESTION:
1. Why do we need include f (ex. 1.0f) in the initialization?
2. why do we need to mention float in the brackets in the formula statement?

Answer 1

thank you

Answer 2

thanks @gordie

Answer 3

but we initialised "a" as a float why we need to add f after 1.0?