using math class in java [closed]

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Closed 9 years ago.

I'm trying to calculate the power of a double to calculate the Quadratic Formula

Here is the code:

private Scanner sc;
double a, b, c;
// Input Coefficients
public void InputCoeff() {
    sc = new Scanner(System.in);

    System.out.println("Please enter the coefficients of this quadratic equation.");
    System.out.println("'ax2 + bx + c = 0'");
    System.out.print("a = ");
    a = sc.nextDouble();
    if(a == 0){
        System.out.println("Coefficient of x2 ('a') can't be zero.");
        System.out.println("Otherwise, it'll be a linear funciton.");
    }
    System.out.print("b = ");
    b = sc.nextDouble();
    System.out.print("c = ");
    c = sc.nextDouble();
}

public void SqRt(double x, double y, double z) {
    double sqrt;
    sqrt = pow(y, 2) - (4 * x * z); // This generates an error
    System.out.println();
}

Why this error?

Thanks.

Answer 1

Change pow to Math.pow. The Math class is a static class, and you need to get the method from the class itself.

Answer 2

Use Math. as prefix to your function pow because pow(double a, double b) is an static method from java.lang.Math class:

public void SqRt(double x, double y, double z) {
    double sqrt;
    sqrt = Math.pow(y, 2) - (4 * x * z); // This generates an error
    System.out.println(sqrt);
}

Also I think you may want to return sqrt from this method so change the return type from void to double and add a return statement in the end as below:

public dobule SqRt(double x, double y, double z) {
    double sqrt;
    sqrt = Math.pow(y, 2) - (4 * x * z); // This generates an error
    System.out.println(sqrt);
        return sqrt;
}

Answer 3

Math.pow is a relative expensive operation to use and also longer to type in many case so I would avoid it if you can. It's much simpler (and faster for you and the computer) use x * x

public static Set<Double> solve(double a, double b, double c) {
    Set<Double> solutions = new TreeSet<Double>();
    double discriminant = b * b - 4 * a * c;
    solutions.add((-b - Math.sqrt(discriminant)) / (2 * a));
    solutions.add((-b + Math.sqrt(discriminant)) / (2 * a));
    solutions.remove(Double.NaN);
    return solutions;
}

public static void main(String... args) {
    System.out.println(solve(1, 3, 2));
    System.out.println(solve(1, 0, -1));
    System.out.println(solve(1, 4, 4));
    System.out.println(solve(1, 0, 1));
}

prints

[-2.0, -1.0]
[-1.0, 1.0]
[-2.0]
[]

Note that you can have none, one or two real solutions.