float returning "NaN"

@Tom_Buck wrote:

So I'm trying to calculate resultant vectors (not vectors as C# and Monogame know them, but physical vectors as in two or more forces acting on an object.). This is all for getting the physics right in my dumb asteroids project. I'm sure my code looks goofy as all get out, but I'm really only concerned with what's written below in the /**/ comments.

I tried to adapt the math in a line of code from here: http://www.fatihtan.net/en/Blog/Post/c-sharp-form-application--calculating-resultant-force-3 into my own project. If I'm doing this all wrong and this class need to be burned with fire, please tell me also, but I feel like I'm very close.

Text formatting here is acting a little goofy as well, but I think it can be deciphered. please go easy on me, I'm a massive noob.

using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace AvoidTheStroids
{
    class Sprite
    {
        private Texture2D _texture;
        private float _rotation;
        private float _dirThrust;
        private float _lastThrust = 0f;
        private float _thrust;
        int butt = 0;

        public Vector2 Position;
        public Vector2 Origin;

        public float RotationVelocity = 3f;
        public float LinearVelocity = 0f;

        //the data below is only meant to be monitored by Game1.cs and displayed to the console
        public float rotation;
        public float dirThrust;
        public float lastThrust;
        public float thrust;
        public Vector2 position;
        public float linearVelocity;


        public Sprite(Texture2D texture)
        {
            _texture = texture;
        }

        public void Update()
        {
            if (Keyboard.GetState().IsKeyDown(Keys.A))
                _rotation -= MathHelper.ToRadians(RotationVelocity);
            if (Keyboard.GetState().IsKeyDown(Keys.D))
                _rotation += MathHelper.ToRadians(RotationVelocity);

            rotation = _rotation;
            dirThrust = _dirThrust;
            lastThrust= _lastThrust;
            thrust = _thrust;
            position = Position;
            linearVelocity = LinearVelocity;

            _dirThrust = 0f;
            if (Keyboard.GetState().IsKeyDown(Keys.W))
            {
                _thrust = .4f;
                _dirThrust = _rotation;
                if (_lastThrust == 0f) _lastThrust = _dirThrust;
            }
            else
            {
                _thrust = 0f;
            }
            //if (Keyboard.GetState().IsKeyDown(Keys.S) && LinearVelocity >= 0)
            //{
            //    LinearVelocity -= .2f;
            //}

            var oneX = (float)Math.Cos(_dirThrust) * _thrust;
            var oneY = (float)Math.Sin(_dirThrust) * _thrust;
            var twoX = (float)Math.Cos(_lastThrust) * LinearVelocity;
            var twoY = (float)Math.Sin(_lastThrust) * LinearVelocity;
            
            if (butt < 2)
            {
                Console.WriteLine(oneX);
                Console.WriteLine(oneY);
                Console.WriteLine(twoX);
                Console.WriteLine(twoY);
            }
            ++butt;

            _lastThrust = (float)Math.Tan((oneX + twoX) / (oneY + twoY));
            LinearVelocity = (float)(Math.Sqrt(Math.Pow((oneX + twoX), 2) + Math.Pow((oneY + twoY), 2)));

           /*
           I'm 100% sure its the line above that is returning "NaN" I found it out through writing the values to the console.
           LinearVelocity initially returns "0" before this line of code happens. I would love to know why.
          */

            if (LinearVelocity > 2f)
            {
                LinearVelocity = 2f;
            }

            var direction = new Vector2((float)Math.Cos(MathHelper.ToRadians(90) - _lastThrust), -(float)Math.Sin(MathHelper.ToRadians(90) - _lastThrust));

            Position += direction * LinearVelocity;
        }

        public void Draw(SpriteBatch spriteBatch)
        {
            spriteBatch.Draw(
                _texture,
                Position,
                null,
                Color.White,
                _rotation,
                Origin,
                1,
                SpriteEffects.None,
                0f);
        }
    }
}

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