Now supposing it was in two dimension supposing the function was function of x and y then of course, it will become function of x0, y0 plus delta x0 you know fx I will just write plus delta y0, fy plus delta x square by2 fxx plus delta y square by2 fyy plus delta x delta y fxy etcetera, you know similar way that we all know that so this is a standard taylor. Now, you see the forces what we go back to this equation relation, we know x, y and n depends on this. Now what we want to know remember now here thus very interesting this concept in important and interesting to know remember now here this is very interesting this concept is important and interesting from all point of view. Initially, the ship is always going along a straight line. So, I have and initial condition, where my u equal to u1 let us say and everything else was 0. I will come back to that so, I know my initial state of a ship moving on a steady state line, it has got certain amount of force on that which also I know because that force is nothing but, a resistance force. Now, what I have done is that I have slightly tilted it given disturbance to it I have slightly made a v and r and v dot and r dot and all that stuff, them my purpose would be to find out what is the additional force coming. Because of that, so see my initial. (เขียน ตัวอย่าง นาทีที่ 16.37)Then, in this case what happened that means u dot equal to v equal to v dot equal to psi dot equal to psi double dot equal to 0 all of them are 0 initially. Also x maybe resistance, even x will be 0 the reason is because, if you take propulsion x becomes 0. If you take propulsion because resistance minus propulsion is 0 but, never mind that let me write it propulsion y is 0, n is 0. That we agree because, obviously it can’t have any y force this side it can’t have any n moment this side . So, when I am going initially I am just going on a straight line. Now, what we have done we have given a non 0 values of this parameters therefore, I want to find out what has happened to my y and x and all that so, what would happen we will start with basically with y. because, x is less important we will just try