1. bn trên lm r
2. lim(x->2) (x^2 - 3x + 2)/(x - 2)
= lim(x->2) (x - 2)(x - 1)/(x - 2)
= lim(x->2) (x - 1)
= 
(bn trên sai r nhé)
3. lim(x->1) (x^2 - 5x + 4)/(x^2 - 1)
= lim(x->1) (x - 1)(x - 4)/(x - 1)(x + 1)
= lim(x->1) (x - 4)/(x + 1)
= -3/2
4. lim(x->+∞) [√(x^2 - 2x + 5) - x]
= lim(x->+∞) x[√(1 - 2/x + 5/x^2) - 1]
ta có lim(x->+∞)  x = +∞
lim(x->+∞) [√(1 - 2/x + 5/x^2) - 1]=0
vay lim(x->+∞) [√(x^2 - 2x + 5) - x] = +∞