I was given the following question: Numerically approximate all critical points of the function f(x,y)=2y(x+2)−x2+y4−9y2.
I cannot figure out how to do this. I tried using a CAS calculator, but ended up with an error.
I know that the critical points are when either partial derivative is undefined or when both partial derivatives are equal to zero. I just cannot figure out how to get those numbers with this function.
I tried graphing it on a handheld ti-nspire cx ii cas and it didn't come up. I tried graphing it on geogebra and got something very weird looking (attached). Can anyone guide me on how to proceed?

I cannot figure out how to do this. I tried using a CAS calculator, but ended up with an error.
I know that the critical points are when either partial derivative is undefined or when both partial derivatives are equal to zero. I just cannot figure out how to get those numbers with this function.
I tried graphing it on a handheld ti-nspire cx ii cas and it didn't come up. I tried graphing it on geogebra and got something very weird looking (attached). Can anyone guide me on how to proceed?
