See we look at this equation, I am going to write this equation in matrix form like A this, this, this. So, what we are writing this equation I have got A 1 d by d t plus A 2, this is one term, B 1 d by d t plus B 2. Here, A 3 d by d t plus A 4 and B 3 d by d t plus B 4. This into V dash r dash equal to 0, 0, this was my equation see this into this pluses this 0 this into this plus. And the characteristic equation is found by taking the determinant of that.