Q/ By using polar Coordinates show that the system below has a limit cycle and show the stability of + his limit cycle: X² = x + x(x² + y² -1) y* = −x + y (x² + y²-1) -x

xy Q/Given H (X,Y) = ex-XX+1 be a first integral find the corresponding system and study the Stability of of critical point of this system.

Q/ show that H (X,Y) = x²-4x-x² is 2 first integral of the system Y° = y 0 y° = 2x + x 3 then study the stability of critical point and draw phase portrait.