I am confused. What is the difference among the problems below? Why aren't they all undefined?
lim x->1 -2x/(1-x) = undefined
lim x->1 x/(1-x)^2 = infinity
lim x-> 3y/(4+4y+y^2) = -infinity
lim x->1 -2x/(1-x) = undefined
lim x->1 x/(1-x)^2 = infinity
lim x-> 3y/(4+4y+y^2) = -infinity