Question as follows f(x,y)=xy , find the level curves for c= +-1,+-2,+-3,+-4,+-5 My first attempt was to set f(x,y)=c c=xy and y=1/x C and this is an hyperbolic function. Is that right? I am also confused what values x can get. I know it is restricted and x>0. Can x get the same value as C ?