9x^2 - 1 # 0 --> x # 1/3 và x # -1/3

Bài 1:

Đặt: \(\left\{{}\begin{matrix}u=\dfrac{1}{2x-2}\\v=\dfrac{1}{y-1}\end{matrix}\right.\) (ĐK: \(x,y\ne1\))  

Hệ trở thành:

\(\Leftrightarrow\left\{{}\begin{matrix}u-v=2\\3u-2v=1\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}3u-3v=6\\3u-2v=1\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}-v=5\\u-v=2\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}v=-5\\u=2+-5\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}v=-5\\u=-3\end{matrix}\right.\)

Trả lại ẩn của hệ pt:

\(\Leftrightarrow\left\{{}\begin{matrix}\dfrac{1}{y-1}=-5\\\dfrac{1}{2x-2}=-3\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}y-1=-\dfrac{1}{5}\\2x-2=-\dfrac{1}{3}\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}y=\dfrac{4}{5}\\x=\dfrac{5}{6}\end{matrix}\right.\left(tm\right)\)

a, \(\sqrt{2x^2-2x+m}=x+1\)

\(\Leftrightarrow\left\{{}\begin{matrix}2x^2-2x+m=x^2+2x+1\\x+1\ge0\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x^2-4x+m-1=0\left(1\right)\\x\ge-1\end{matrix}\right.\)

Yêu cầu bài toán thỏa mãn khi phương trình \(\left(1\right)\) có nghiệm \(x\ge-1\) chỉ có thể xảy ra các trường hợp sau

TH1: \(x_1\ge x_2\ge-1\)

\(\Leftrightarrow\left\{{}\begin{matrix}\Delta'\ge0\\\dfrac{x_1+x_2}{2}\ge-1\\1.f\left(-1\right)\ge0\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}5-m\ge0\\2\ge-1\\m+4\ge0\end{matrix}\right.\)

\(\Leftrightarrow-4\le m\le5\)

TH2: \(x_1\ge-1>x_2\)

\(\Leftrightarrow\left\{{}\begin{matrix}5-m\ge0\\m+4< 0\end{matrix}\right.\)

\(\Rightarrow\) vô nghiệm

Vậy \(-4\le m\le5\)

\(\sqrt{2x^2-2x+1}=2x-1\)

\(\Leftrightarrow2x^2-2x+1=4x^2-4x+1\)

\(\Leftrightarrow2x^2-2x=0\)

\(\Leftrightarrow2x\left(x-1\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=1\\x=0\end{matrix}\right.\)

Vậy S=\(\left\{0,1\right\}\)

ĐKXĐ:

\(\left\{{}\begin{matrix}2x^2-2x+1\ge0\\2x-1\ge0\end{matrix}\right.\)\(\Leftrightarrow\left\{{}\begin{matrix}\left(x-1\right)^2+x^2\ge0\forall x\\x\ge\dfrac{1}{2}\end{matrix}\right.\)

Đề bài

\(\Rightarrow2x^2-2x+1=\left(2x-1\right)^2=4x^2-4x+1\)

\(\Leftrightarrow2x^2-2x=0\)

\(\Leftrightarrow2x\left(x-1\right)=0\Leftrightarrow\left[{}\begin{matrix}x=0\left(ktm\right)\\x=1\left(tm\right)\end{matrix}\right.\)

Vậy pt có tập nghiệm \(S=\left\{1\right\}\)

Ta có: \(\sqrt{2x^2-2x+1}=2x-1\)

\(\Leftrightarrow4x^2-4x+1-2x^2+2x-1=0\)

\(\Leftrightarrow2x\left(x-1\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=0\left(loại\right)\\x=1\left(nhận\right)\end{matrix}\right.\)

PT: \(\sqrt{2x+2\sqrt{2x-1}}-\sqrt{2x-2\sqrt{2x-1}}=\sqrt{2x-1}-10\) (1) (ĐK: \(x\ge\dfrac{1}{2}\)) 

Đặt: \(y=\sqrt{2x-1}\) (ĐK: \(y\ge0\)) 

\(\Leftrightarrow x=\dfrac{y^2+1}{2}\)  

Thay vào (1) ta có: 

\(\sqrt{2\cdot\dfrac{y^2+1}{2}+2y}-\sqrt{2\cdot\dfrac{y^2+1}{2}-2y}=y-10\)

\(\Leftrightarrow\sqrt{y^2+1+2y}-\sqrt{y^2+1-2y}=y-10\)

\(\Leftrightarrow\sqrt{\text{ }y^2+2y+1}-\sqrt{y^2-2y+1}=y-10\)

\(\Leftrightarrow\sqrt{\left(y+1\right)^2}-\sqrt{\left(y-1\right)^2}=y-10\)   

\(\Leftrightarrow\left|y+1\right|-\left|y-1\right|=y-10\)

TH1: Với: \(0\le y< 1\) 

\(\Leftrightarrow y+1-1+y=y-10\)

\(\Leftrightarrow2y-y=-10\)

\(\Leftrightarrow y=-10\left(ktm\right)\)

TH2: \(y\ge1\)

\(\Leftrightarrow y+1-y+1=y-10\)

\(\Leftrightarrow2=y-10\)

\(\Leftrightarrow y=10+2\)

\(\Leftrightarrow y=12\left(tm\right)\)

Mà: y=12

\(\Rightarrow x=\dfrac{12^2+1}{2}=\dfrac{145}{2}\left(tm\right)\) 

Vậy: ...

x = 145/2

a, đk : x >= 1

\(\left[{}\begin{matrix}3x+5=2x-2\\3x+5=2-2x\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-7\\x=-\dfrac{3}{5}\end{matrix}\right.\left(ktm\right)\)

vậy pt vô nghiệm 

b, đk >= 0 

\(\left[{}\begin{matrix}x^2+1=2x\\x^2+1=-2x\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}\left(x-1\right)^2=0\\\left(x+1\right)^2=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=1\left(tm\right)\\x=-1\left(ktm\right)\end{matrix}\right.\)

c, \(\left[{}\begin{matrix}2x^2+2x=0\\2x^2+4x+2=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}2x\left(x+1\right)=0\\x^2+2x+1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0;x=-1\\x=-1\end{matrix}\right.\)

ta có : x^5+2x^4+3x^3+3x^2+2x+1=0

\(\Leftrightarrow\)x^5+x^4+x^4+x^3+2x^3+2x^2+x^2+x+x+1=0

\(\Leftrightarrow\)(x^5+x^4)+(x^4+x^3)+(2x^3+2x^2)+(x^2+x)+(x+1)=0

\(\Leftrightarrow\)x^4(x+1)+x^3(x+1)+2x^2(x+1)+x(x+1)+(x+1)=0

\(\Leftrightarrow\)(x+1)(x^4+x^3+2x^2+x+1)=0

\(\Leftrightarrow\)(x+1)(x^4+x^3+x^2+x^2+x+1)=0

\(\Leftrightarrow\)(x+1)[x^2(x^2+x+1)+(x^2+x+1)]=0

\(\Leftrightarrow\)(x+1)(x^2+x+1)(x^2+1)=0

VÌ x^2+x+1=(x+\(\dfrac{1}{2}\))^2+\(\dfrac{3}{4}\)\(\ne0\) và x^2+1\(\ne0\)

\(\Rightarrow\)x+1=0

\(\Rightarrow\)x=-1

CÒN CÂU B TỰ LÀM (02042006)

b: x^4+3x^3-2x^2+x-3=0

=>x^4-x^3+4x^3-4x^2+2x^2-2x+3x-3=0

=>(x-1)(x^3+4x^2+2x+3)=0

=>x-1=0

=>x=1