Question

tìm x biết 

a) \(\left|2x-7\right|=3\)

b) \(\left|21x-5\right|=\left|3x-7\right|\)

c) \(\left|7-2x\right|=1-3x\)

d) \(\left|x^2+3x\right|+\left|x^2+4x+3\right|=0\)

Answer 1

b)\(\left|21x-5\right|=\left|3x-7\right|\)

\(\Leftrightarrow\begin{cases}21x-5=3x-7\\21x-5=7-3x\end{cases}\)

\(\Leftrightarrow\begin{cases}9x=-1\\24x=12\end{cases}\)

\(\Leftrightarrow\begin{cases}x=-\frac{1}{9}\\x=\frac{1}{2}\end{cases}\)

Answer 2

a)\(\left|2x-7\right|=3\)

\(\Rightarrow2x-7=\pm3\)

Nếu \(2x-7=3\)

\(\Rightarrow2x=10\)

\(\Rightarrow x=5\)

Nếu \(2x-7=-3\)

\(\Rightarrow2x=4\)

\(\Rightarrow x=2\)

Answer 3

c)\(\left|7-2x\right|=1-3x\)

\(\Rightarrow7-2x=\pm\left(1-3x\right)\)

Nếu \(7-2x=1-3x\)

\(\Rightarrow x=-6\)

Nếu \(7-2x=-\left(1-3x\right)\)

\(\Rightarrow7-2x=-1+3x\)

\(\Rightarrow5x=8\)

\(\Rightarrow x=\frac{8}{5}\)

 

 

Answer 4

d)|x²+3x|+|x²+4x+3|=0

=>|x²+3x|=-|x²+4x+3|

Vì \(\left|x^2+3x\right|\ge0>VP\)

=>ko tồn tại x thỏa mãn

Answer 5

a) \(\left\{\begin{matrix}2x-7=3\\2x-7=-3\end{matrix}\right.\Rightarrow\left\{\begin{matrix}2x=10\\2x=4\end{matrix}\right.\Rightarrow}\left\{\begin{matrix}x=5\\x=2\end{matrix}\right.\)