2) lim=$\frac{1-\frac{1}{3^n}}{(\frac{2}{3})^n-2+\frac{1}{3^n}}=\frac{-1}{2}$
3) limf(x) x->$2^+$= $\frac{(x-1)(x-2)}{x(x-2)}=\frac{x-1}{x}=\frac{1}{2}$
limf(x) x->$2^-$=3m+1
liên tục tại x=2 khi 3m+1=1/2
=> m=-1/6
4) y'=$3-12x^2$
x=0 => y=0
=> PTTT là
y=f'(0)(x-0)+0
=>y=3x