The first 1 you can substitute.

The third one you get (SOMETHING)/0 where SOMETHING

not = zero. Thus it is + infinity.

The second one you get 0/0 which is bad.

You factor,

x^3-3x^2+4

x^3-2x^2+4-x^2

x^2(x-2)+(2-x)(2+x)

x^2(x-2)-(x-2)(x+2)

(x-2)(x^2-x-2)

Now you can cancel (x-2) to get,

x^2-x-2 and take limit as x -- > 0