(-)Lan won't buy it next month

(?)Did you go to your friend's house yesterday?

officially

modernized

equality

friendliness

inconvenience

religious

played

has been

was doing

haven't finished

(-)She doesn't go to school everyday.

(?) Does she go to school everyday? 

Để\(\sqrt{x^2-1}\)có nghĩa

\(\Rightarrow x^2-1\ge0\)

\(\Leftrightarrow x^2\ge1\)

\(\Leftrightarrow\left|x\right|\ge1\)

\(\Leftrightarrow|^{x\ge1}_{x\le-1}\)

Vậy.....

Ý chí và quyết Chí.

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