Find and sort all of the extremum of $f(x,y) = |3x| + x^4y^2$
not quite sure what to do with the absolute value of $|3x|$ , should i separate it to two options? , one for $3x>0$ and the other option for $3x<0$ ?
from $f(x,y) = |3x| + x^4y^2= 3|x| + |x|^4|y|^2$ I think you can discuss with $x\geq0$ and $y\geq0$ in $f(x,y) = 3x + x^4y^2$.
with the second $x=0$ or $y=0$ which both are impossible as conflict with the first, remains $$f(x,y) = |3x| + x^4y^2= 3|x| + |x|^4|y|^2\geq0=f(0,0)$$ specifies the only minimum point in the origin.