Cho tam giác đều $ABC$ cạnh $a$. Tính tích vô hướng $\overrightarrow{AB}\cdot\overrightarrow{AC}$.

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Một số câu hỏi khác có thể bạn quan tâm.

• Choose a word that has different stress pattern:

  uncomfortable             conversation             embarrassing           experience

• Choose the word that has the underlined part pronounced differently from the rest:

  passed             treated            hoped              noticed

• Choose the best answer for the following sentence:

  I have invited some friends to our house for _____________________________ dinner.

• Choose the best answer for the following sentence:

  My most ___________________________ moment was trying to introduce a woman whose name I couldn't remember.

• Choose the best answer for the following sentence:

  She ______________________ to get her breath back and then carried on jogging.

    

• Choose the best answer for the following sentence:

  The more they tried to get her to talk about her experiences, the further she

  retreated back into her __________________________ .

    

• Choose the best answer for the following sentence: 

  The manager  _________________________ and ______________________ you in a few minutes.

   

• Choose the best answer for the following sentence: 

  Water when _______________________ always __________________________ off steam.

   

• Choose the best answer for the following sentence:

  Since the ditch is full of water, ___________________________ last night.

   

• Choose one sentence that has the same meaning as the root one:

  We should eat more fruit and vegetables to prevent ourselves from cancer.