Cho hai tập hợp A,BA,B. Điền vào ô trống mệnh đề thích hợp:

  \Leftrightarrow\left\{{}\begin{aligned}x\in A\\x\in B\end{aligned}\right..⇔{x∈Ax∈B​.

  \Leftrightarrow\left[{}\begin{aligned}x\in A\\x\in B\end{aligned}\right..⇔[x∈Ax∈B​.

  \Leftrightarrow\left\{{}\begin{aligned}x\in A\\x\notin B\end{aligned}\right..⇔{x∈Ax∈/B​.

Xác định $a,b,c$, biết parabol $y=a{x}^2+bx+c$ đi qua điểm $A(8;0)$ và có đỉnh $I(6;-12)$.

Cấm cop mạng

Part II: Think about this idea:

Many children do not get enough exercise. This is why all children should be required to play sports in school.

Write only an introduction to an essay about this topic. Remember that an introduction should have a few facts about the idea, but not arguments. Write an introduction of at least 50 words.