using System;

public class Program

{

    public static void Main()

    {

        Program pg = new Program();

        Console.WriteLine("Hello World");

        double aX = 10, aY = 15;

        double mX = 15, mY = 10;

        double width = 100, height = 100;

        double centerX = width/2, centerY = height/2;

        double scalProd = pg.ScalarProduct(aX, aY, mX, mY);

        double aMag = pg.VecMagnitude(aX, aY);

        double mMag = pg.VecMagnitude(mX, mY);

        double grad = pg.AngleBetweenVectors(scalProd, aMag, mMag);

    }

    public double ScalarProduct(double aX, double aY, double bX, double bY){

        double scalProd = (aX * bX) + (aY*bY);

        return scalProd;

    }

    public double VecMagnitude(double aX, double aY){

        double mag = Math.Sqrt(((aX*aX) + (aY*aY)));

        return mag;

    }

    public double AngleBetweenVectors(double scalProd, double aMag, double bMag){

        double grad = Math.Acos(scalProd / (aMag*bMag)); 

        return grad;

    }

    public void RotateVector(double rVecX, double rVecY, double oVecX, double oVecY, double rad)

    {

        rVecX = (Math.Cos(rad) * oVecX) - (Math.Sin(rad) * oVecY);

        rVecY = (Math.Sin(rad) * oVecX) + (Math.Cos(rad) * oVecY);

    }

}