Question

tìm x, biết

-2(-3-4x)-3(3x-7)=31

10.(x-7)=8.(x-4)+x

2.|x-1|=3.(5-1)

2(x+3)-2(x-3)=x

(x+3)(x-4)=0

Answer 1

Bài 1 :                                         Bài giải

\(-2\left(-3-4x\right)-3\left(3x-7\right)=31\)

\(6+8x-9x-21=31\)

\(-x-15=31\)

\(-x=31+15\)

\(-x=46\)

\(x=-46\)

b, \(10\left(x-7\right)=8\left(x-4\right)+x\)

\(10x-70=8x-32+x\)

\(10x-70=9x-32\)

\(10x-9x=-32+70\)

\(x=38\)

c, \(2\left|x-1\right|=3\cdot\left(5-1\right)\)

\(2\left|x-1\right|=15-3\)

\(2\left|x-1\right|=12\)
\(\left|x-1\right|=12\text{ : }2\)

\(\left|x-1\right|=6\)

\(\Rightarrow\orbr{\begin{cases}x-1=-6\\x-1=6\end{cases}}\Rightarrow\orbr{\begin{cases}x=-5\\x=7\end{cases}}\)

\(\Rightarrow\text{ }x\in\left\{-5\text{ ; }7\right\}\)

d, \(2\left(x+3\right)-2\left(x-3\right)=x\)

\(2\left(x+3-x-3\right)=x\)

\(2\cdot0=x\)

\(x=0\)

e, \(\left(x+3\right)\left(x-4\right)=0\)

\(\Rightarrow\orbr{\begin{cases}x+3=0\\x-4=0\end{cases}}\Rightarrow\orbr{\begin{cases}x=-3\\x=4\end{cases}}\)

\(\Rightarrow\text{ }x\in\left\{-3\text{ ; }4\right\}\)

Answer 2

a, \(-2\left(-3-4x\right)-3\left(3x-7\right)=31\)

\(6+8x-9x-21=31\)

\(-x-15=31\)

\(-x=31+15\)

\(-x=46\)

\(x=-46\)

b, \(10\left(x-7\right)=8\left(x-4\right)+x\)

\(10x-70=8x-32+x\)

\(10x-70=9x-32\)

\(10x-9x=-32+70\)

\(x=38\)

c, \(2\left|x-1\right|=3\cdot\left(5-1\right)\)

\(2\left|x-1\right|=15-3\)

\(2\left|x-1\right|=12\)
\(\left|x-1\right|=12\text{ : }2\)

\(\left|x-1\right|=6\)

\(\Rightarrow\orbr{\begin{cases}x-1=-6\\x-1=6\end{cases}}\Rightarrow\orbr{\begin{cases}x=-5\\x=7\end{cases}}\)

\(\Rightarrow\text{ }x\in\left\{-5\text{ ; }7\right\}\)

d, \(2\left(x+3\right)-2\left(x-3\right)=x\)

\(2\left(x+3-x-3\right)=x\)

\(2\cdot0=x\)

\(x=0\)

e, \(\left(x+3\right)\left(x-4\right)=0\)

\(\Rightarrow\orbr{\begin{cases}x+3=0\\x-4=0\end{cases}}\Rightarrow\orbr{\begin{cases}x=-3\\x=4\end{cases}}\)

\(\Rightarrow\text{ }x\in\left\{-3\text{ ; }4\right\}\)