Question

tìm x biết:

a) |1/3x|.|-2,7|=|-9|

b) |x+1|>2

Answer 1

a) \(\left|\dfrac{1}{3}x\right|.\left|-2,7\right|=\left|-9\right|\)

\(\left|\dfrac{1}{3}x\right|.2,7=9\)

\(\left|\dfrac{1}{3}x\right|=9:2,7=\dfrac{10}{3}\)

\(\Rightarrow\left\{{}\begin{matrix}\dfrac{1}{3}x=\dfrac{10}{3}\\\dfrac{1}{3}x=-\dfrac{10}{3}\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=10\\x=-10\end{matrix}\right.\)

Answer 2

a) \(\left|\dfrac{1}{3}x\right|\cdot\left|-2,7\right|=\left|-9\right|\)

\(\Rightarrow\dfrac{1}{3}\cdot\left|x\right|\cdot2,7=9\)

\(\Leftrightarrow\dfrac{1}{3}\cdot\left|x\right|\cdot\dfrac{27}{10}=9\)

\(\Leftrightarrow\left|x\right|\cdot\dfrac{9}{10}=9\)

\(\Leftrightarrow\dfrac{9}{10}\cdot\left|x\right|=9\)

\(\Leftrightarrow\left|x\right|=10\)

\(\Rightarrow\left[{}\begin{matrix}x=10\\x=-10\end{matrix}\right.\)

Vậy \(x_1=-10;x_2=10\)

b) \(\left|x+1\right|>2\)

dễ tự giải

Answer 3

b) \(\left|x+1\right|>2\Leftrightarrow\left[{}\begin{matrix}x+1>2\\x+1< -2\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x>1\\x< -3\end{matrix}\right.\)

Vậy giá trị x thỏa mãn đề bài .......

Answer 4

a) \(\left|\dfrac{1}{3}x\right|.\left|-2,7\right|=\left|-9\right|\)

\(\Rightarrow\left|\dfrac{1}{3}x\right|.\left(2,7\right)=9\)

\(\Leftrightarrow\left|\dfrac{1}{3}x\right|=9:\left(2,7\right)\)

\(\Rightarrow\left|\dfrac{1}{3}x\right|=\dfrac{10}{3}\)

\(\Rightarrow\left[{}\begin{matrix}\dfrac{1}{3}x=\dfrac{10}{3}\\\dfrac{1}{3}x=-\dfrac{10}{3}\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=10\\x=-10\end{matrix}\right.\)

Vậy \(x_1=10;x_2=-10\)

b) \(\left|x+1\right|>2\)

\(\Rightarrow\left[{}\begin{matrix}x+1>2\\x+1< -2\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x>1\\x< -3\end{matrix}\right.\)