mn xem giúp em nhanh nhanh dc ko ạ em dag cần gấp

a) \(\frac{21}{x}=\frac{7}{4}\Rightarrow x=\frac{21.4}{7}=12\)

     \(\frac{y}{16}=\frac{7}{4}\Rightarrow y=\frac{16.7}{4}=28\)

      \(\frac{-14}{z}=\frac{7}{4}\Rightarrow x=\frac{\left(-14\right).4}{7}=-8\)

Vậy ...

b) \(\frac{-21}{x}=\frac{-3}{4}\Rightarrow x=\frac{\left(-21\right).4}{-3}=28\)

     \(\frac{y}{-16}=\frac{-3}{4}\Rightarrow y=\frac{\left(-16\right).\left(-3\right)}{4}=12\)

      \(\frac{81}{z}=\frac{-3}{4}\Rightarrow z=\frac{81.4}{-3}=-108\)

\(x^2+5x+6\ge0\)

\(\Leftrightarrow x^2+2x+3x+6\ge0\)

\(\Leftrightarrow x\left(x+2\right)+3\left(x+2\right)\ge0\)

\(\Leftrightarrow\left(x+2\right)\left(x+3\right)\ge0\)

\(\Leftrightarrow\hept{\begin{cases}x+2\ge0\\x+3\ge0\end{cases}}\) hoặc \(\hept{\begin{cases}x+2\le0\\x+3\le0\end{cases}}\)

\(\Leftrightarrow\hept{\begin{cases}x\ge-2\\x\ge-3\end{cases}}\)   hoặc    \(\hept{\begin{cases}x\le-2\\x\le-3\end{cases}}\)

Vậy \(x\ge-2\) hoặc \(x\le-3\)

\(x^2+5x+6\ge0\)

<=>  \(\left(x+2\right)\left(x+3\right)\ge0\)

TH1:  \(\hept{\begin{cases}x+2\ge0\\x+3\ge0\end{cases}}\)<=>   \(\hept{\begin{cases}x\ge-2\\x\ge-3\end{cases}}\)<=>  \(x\ge-2\)

TH2:  \(\hept{\begin{cases}x+2\le0\\x+3\le0\end{cases}}\)<=>   \(\hept{\begin{cases}x\le-2\\x\le-3\end{cases}}\)<=>  \(x\le-3\)

Vậy....

2000

4000

6000

8000

10000

k bn

1000 + 1000 = 2000

2000 + 2000 = 4000

3000 + 3000 = 6000

4000 + 4000 = 8000

5000 + 5000 = 10000

kb nha

20 nha. Học tốt!

10 + 10 = 20

Tk nha!!