\(=\left(\dfrac{7}{4}.\dfrac{2}{7}\right).\dfrac{4}{5}=\dfrac{1}{2}.\dfrac{4}{5}=\dfrac{2}{5}\)

a/\(\left(1,75:\dfrac{7}{2}\right).\dfrac{4}{5}=\left(\dfrac{7}{4}:\dfrac{7}{2}\right).\dfrac{4}{5}=\dfrac{1}{2}.\dfrac{4}{5}\dfrac{2}{5}\)

A nha

nhớ tick cho mik <3

5B

6A

Câu 5 : B

Câu 6: D

Câu 4:B

Câu 5:A

4b vì góc tới bằng góc phản xạ nên lấy 80/2=40

b: \(\Leftrightarrow x+\dfrac{2}{5}=\dfrac{2}{3}\)

hay \(x=\dfrac{1}{15}\)

1. illegal

2. traffic jam

3. seatbelt

4. safely

5. railway station

6. safety

7. traffic signs

8. helicopter

9. tricycle

10. boat

\(c,\left\{{}\begin{matrix}-4x+ay=1+a\\\left(6+a\right)x+2y=3+b\end{matrix}\right.\)

Để hpt có nghiệm duy nhất \(\Leftrightarrow\dfrac{-4}{6+a}\ne\dfrac{a}{2}\Leftrightarrow a^2+6a+8\ne0\Leftrightarrow\left\{{}\begin{matrix}a\ne-2\\a\ne-4\end{matrix}\right.\)

Để hpt vô nghiệm \(\Leftrightarrow\dfrac{-4}{6+a}=\dfrac{a}{2}\ne\dfrac{1+a}{3+b}\)

\(\Leftrightarrow\left\{{}\begin{matrix}\dfrac{-4}{6+a}=\dfrac{a}{2}\\\dfrac{a}{2}\ne\dfrac{1+a}{3+b}\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}\left[{}\begin{matrix}a=-2\\a=-4\end{matrix}\right.\\2+2a\ne3a+ab\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}\left[{}\begin{matrix}a=-2\\a=-4\end{matrix}\right.\\a\ne2-ab\end{matrix}\right.\)

Để hpt có vô số nghiệm \(\Leftrightarrow\dfrac{-4}{6+a}=\dfrac{a}{2}=\dfrac{1+a}{3+b}\)

\(\Leftrightarrow\left\{{}\begin{matrix}\dfrac{-4}{6+a}=\dfrac{a}{2}\\\dfrac{a}{2}=\dfrac{1+a}{3+b}\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}\left[{}\begin{matrix}a=-2\\a=-4\end{matrix}\right.\\2+2a=3a+ab\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}\left[{}\begin{matrix}a=-2\\a=-4\end{matrix}\right.\\a=2-ab\end{matrix}\right.\)

A

A

Câu A

\(\dfrac{12x4x72}{36x2x9}=\dfrac{48x72}{72x9}=\dfrac{48}{9}=\dfrac{16}{3}\)