3.(2X+3)=-X.(X-2)-1 <=>6X+9=-\(x^2\)+2X-1 <=> \(x^2\) +4x+10=0 (\(\Delta\)' =4-10=-6 nhỏ hơn 0)

pt vô nghiệm

a)

\(\left\{{}\begin{matrix}x-2y=-1\\3x-4y=9\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=2y-1\\3\left(2y-1\right)-4y=9\end{matrix}\right.\Leftrightarrow}\left\{{}\begin{matrix}x=2y-1\\y=6\end{matrix}\right.\Leftrightarrow}\left\{{}\begin{matrix}x=11\\y=6\end{matrix}\right.\)

\(\left\{{}\begin{matrix}x-2y=-1\\3x-4y=9\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=2y-1\\3\left(2y-1\right)-4y=9\end{matrix}\right.\left\{{}\begin{matrix}x=11\\y=6\end{matrix}\right.\)

\(x^2-8x+16=0\Leftrightarrow\left(x-4\right)^2=0\Leftrightarrow x=4\)

a, ĐKXĐ: ...

\(\sqrt{3x^2-2x+6}+3-2x=0\)

\(\Leftrightarrow\sqrt{3x^2-2x+6}=2x-3\)

\(\Leftrightarrow3x^2-2x+6=4x^2-12x+9\)

\(\Leftrightarrow4x^2-10x+3=0\)

.....

b, ĐKXĐ: ...

\(\sqrt{x+1}+\sqrt{x-1}=4\\ \Leftrightarrow x+1+x-1+2\sqrt{\left(x+1\right)\left(x-1\right)}=16\\ \Leftrightarrow2\sqrt{x^2-1}=16-2x\\ \Leftrightarrow\sqrt{x^2-1}=8-x\\ \Leftrightarrow x^2-1=64-16x+x^2\\ \Leftrightarrow65-16x=0\\ \Leftrightarrow x=\dfrac{65}{16}\)

1. A

2. C 

Câu 1: A

Câu 2: C

Câu 2: 

`3x^2-2x=x^2+3`

`<=>3x^2-x^2-2x-3=0`

`<=>2x^2-2x-3=0`

Ptr có: `\Delta'=(-1)^2-2.(-3)=7 > 0`

  `=>`Ptr có `2` nghiệm pb

`=>{(x_1=[-b'+\sqrt{\Delta'}]/a=[1+\sqrt{7}]/2),(x_1=[-b'-\sqrt{\Delta'}]/a=[1-\sqrt{7}]/2):}`

Ta có: \(\dfrac{2x+1}{6}-\dfrac{x-2}{4}=\dfrac{3-2x}{3}-x\)

\(\Leftrightarrow4x+2-3x+6=12-8x-12x\)

\(\Leftrightarrow x+8+20x-12=0\)

\(\Leftrightarrow x=\dfrac{4}{21}\)