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!!

a)

\(5^{2222}=\left(5^2\right)^{1111}=25^{1111}\)

\(2^{5555}=\left(2^5\right)^{1111}=32^{1111}\)

=> tự kết luận

b)

ĐỀ ?????

a)  \(5^{2222}=5^{2.1111}=25^{1111}\)

      \(2^{5555}=2^{5.1111}=32^{1111}\)

Do  \(25^{1111}< 32^{1111}\)nên    \(5^{2222}< 2^{5555}\)

b)  \(4a=3b\)=>   \(\frac{a}{3}=\frac{b}{4}\)

Áp dụng t.c dãy tỉ số bằng nhau ta có:

\(\frac{a}{3}=\frac{b}{4}=\frac{a+b}{3+4}=\frac{21}{7}=3\)

suy ra:  \(\frac{a}{3}=3\)=>  \(a=9\)

             \(\frac{b}{4}=3\)=>   \(b=21\)

Vậy....

1, ..... up .............

2, ....... up.................

3, ......over........

  ~ chúc bạn học tốt ~ k mk

1 We changed the hotels because we couldn't put up with the noise

2 They brought that child away very badly.She is so spoilt

3 She has just been taken such as a shop-assistant