Привет. У меня проблема с пестремой, помогите пожалуйста:

restart;
y:=sqrt((x^2*(x^2-4))/(x^2-1));
readlib(extrema): readlib(maximize): readlib(minimize):
extrema(y,{},x,'s');s;

ymax:=maximize(y,{x});
Error, (in maximization) unexpected parameters: {x}

ymin:=minimize(y,{x});
Error, (in minimization) unexpected parameters: {x}

Hello. I have a problem with the phaseportrait and I hope could help me with this: