Câu 1: $A=\dfrac{(1-x)^6 -\sqrt[6]{1+x}}{x}$ đặt $\sqrt[6]{1+x}=t \Rightarrow x= t^6-1$ khi đó $t \to 1$
$A=\dfrac{(2-t)^6-t^6}{t^6-1} =\dfrac{-4 (t-1) (3 t^4-12 t^3+28 t^2-32 t+16)}{(t-1)(t^5 + t^4+...+t+1)}$
$\lim \limits_{t\to 1} A= \lim \limits_{t\to 1} \dfrac{-4 (3 t^4-12 t^3+28 t^2-32 t+16)}{t^5 + t^4+...+t+1} =-2$