3) \(\frac{x-2}{x-5}-\frac{5}{x^2-5x}=\frac{1}{x}\)

\(\Leftrightarrow\frac{x-2}{x-5}-\frac{5}{x.\left(x-5\right)}=\frac{1}{x}\)

\(\Leftrightarrow\frac{x.\left(x-2\right)}{x.\left(x-5\right)}-\frac{5}{x.\left(x-5\right)}=\frac{1.\left(x-5\right)}{x.\left(x-5\right)}\)

Mc: \(x.\left(x-5\right)\)

\(\Leftrightarrow\) \(x^2\) - 2\(x\) - 5 = \(x\) - 5

\(\Leftrightarrow\) \(x^2\) - 2\(x\) - \(x\) - 5 + 5 = 0

\(\Leftrightarrow\) \(x^2\) - 3\(x\) = 0

\(\Leftrightarrow\) \(x\) . (\(x\) - 3) = 0

\(\Leftrightarrow\) \(x\) = 0 hoặc \(x\) - 3 = 0

\(\Leftrightarrow\) \(x\) = 0 hoặc \(x\) = 3

Vậy \(x\) = 0 hoặc \(x\) = 3

\(x-5\ne0\Rightarrow x\ne5\)

\(x^2-5\ne0\Rightarrow x\ne5\) và \(x\ne0\) \(\Rightarrow\left\{{}\begin{matrix}x\ne0\\x\ne5\end{matrix}\right.\)

\(x\ne0\)

Vậy S = {3}

4) \(\frac{x-4}{x+7}-\frac{1}{x}=\frac{-7}{x^2+7x}\)

\(\Leftrightarrow\frac{x-4}{x+7}-\frac{1}{x}=\frac{-7}{x.\left(x+7\right)}\)

\(\Leftrightarrow\frac{x.\left(x-4\right)}{x.\left(x+7\right)}-\frac{1.\left(x+7\right)}{x.\left(x+7\right)}=\frac{-7}{x.\left(x+7\right)}\)

Mc: \(x.\left(x+7\right)\)

\(\Leftrightarrow x^2-4x-x-7=-7\)

\(\Leftrightarrow x^2-4x-x=-7+7\)

\(\Leftrightarrow\) \(x^2-5x=0\)

\(\Leftrightarrow x.\left(x-5\right)=0\)

\(\Leftrightarrow x=0\) hoặc \(x-5=0\)

\(\Leftrightarrow x=0\) hoặc \(x=5\)

Vậy \(x=0\) hoặc \(x=5\)

\(x+7\ne0\Rightarrow x\ne-7\)

\(x^2+7\ne0\Rightarrow x\ne-7\) và \(x\ne0\) \(\Rightarrow\left\{{}\begin{matrix}x\ne0\\x\ne-7\end{matrix}\right.\)

\(x\ne0\)

Vậy S = {5}

5) \(\frac{x+2}{x-2}+\frac{x-2}{x+2}=\frac{8x}{x^2-4}\)

\(\left\{{}\begin{matrix}x-2\ne0\\x+2\ne0\\x^2-4\ne0\end{matrix}\right.\Rightarrow TXĐ\left\{{}\begin{matrix}x\ne2\\x\ne-2\end{matrix}\right.\)

Mc : \(\left(x-2\right).\left(x+2\right)\)

\(\Leftrightarrow\frac{\left(x+2\right).\left(x+2\right)}{\left(x-2\right).\left(x+2\right)}+\frac{\left(x-2\right).\left(x-2\right)}{\left(x+2\right).\left(x-2\right)}=\frac{8x}{\left(x-2\right).\left(x+2\right)}\)

\(\Leftrightarrow x^2+2x+2x+4+x^2-2x-2x+4=8x\)

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

\(\Leftrightarrow2x^2-8x+8=0\)

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

\(\Leftrightarrow\) \(2x.\left(x-2\right)-4.\left(x-2\right)=0\)

\(\Leftrightarrow\left(2x-4\right).\left(x-2\right)=0\)

\(\Leftrightarrow2x-4=0\) hoặc \(x-2=0\)

\(\Leftrightarrow x=2\) hoặc \(x=2\)

\(\Leftrightarrow x=2\) (Loại) hoặc x = 2 (Loại)

Vậy S = \(\left\{\varnothing\right\}\)

6) \(\frac{x+1}{x-1}-\frac{x-1}{x+1}=\frac{4}{x^2-1}\)

\(\Leftrightarrow\frac{\left(x+1\right).\left(x+1\right)}{\left(x-1\right).\left(x+1\right)}-\frac{\left(x-1\right).\left(x-1\right)}{\left(x+1\right).\left(x-1\right)}=\frac{4}{\left(x-1\right).\left(x+1\right)}\)

MC: \(\left(x-1\right).\left(x+1\right)\)

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

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

\(\Leftrightarrow4x-4=0\)

\(\Leftrightarrow4.\left(x-1\right)=0\)

\(\Leftrightarrow\) 4 = 0 hoặc \(x-1=0\)

\(\Leftrightarrow\) 4 = 0 hoặc \(x=1\)

\(\Leftrightarrow\) 4 = 0 (Loại) hoặc \(x=1\) (Loại)

Vậy S = \(\left\{\varnothing\right\}\)

7) \(\frac{x+1}{x-1}+\frac{-4x}{x^2-1}=\frac{x-1}{x+1}\)

\(\Leftrightarrow\frac{\left(x+1\right).\left(x+1\right)}{\left(x-1\right).\left(x+1\right)}+\frac{-4x}{\left(x-1\right).\left(x+1\right)}=\frac{\left(x-1\right).\left(x-1\right)}{\left(x+1\right).\left(x-1\right)}\)

\(Mc:\left(x-1\right).\left(x+1\right)\)

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

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

\(\Leftrightarrow0=0\) (Nhận)

Vậy S = \(\left\{x\in R;x\ne\pm1\right\}\)

a) \(\frac{x-23}{24}+\frac{x-23}{25}=\frac{x-23}{26}+\frac{x-23}{27}\)

\(\Leftrightarrow\frac{x-23}{24}+\frac{x-23}{25}-\frac{x-23}{26}-\frac{x-23}{27}=0\)

\(\Leftrightarrow\left(x-23\right)\left(\frac{1}{24}+\frac{1}{25}-\frac{1}{26}-\frac{1}{27}\right)=0\)

\(\Leftrightarrow x-23=0\)( vì \(\frac{1}{24}+\frac{1}{25}-\frac{1}{26}-\frac{1}{27}\ne0\))

\(\Leftrightarrow x=23\)

Vậy nghiệm của pt x=23

a) \(1+\sqrt{3x+1}=3x\)

ĐKXĐ: \(3x+1\ge0\Leftrightarrow x\ge\frac{-1}{3}\)

\(\Rightarrow\sqrt{3x+1}=3x-1\)

\(\Leftrightarrow\left(\sqrt{3x+1}\right)^2=\left(3x-1\right)^2\)

\(\Leftrightarrow3x+1=9x^2-6x+1\)

\(\Leftrightarrow9x^2-9x=0\)

\(\Leftrightarrow9x\left(x-1\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}x=0\\x-1=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=0\\x=1\end{cases}}}\)(tm)

Vậy tập nghiệm của phương trình là \(S=\left\{0;1\right\}\)

b) \(\sqrt{\frac{5x+7}{x+3}}=4\)

ĐKXĐ: \(\hept{\begin{cases}\frac{5x+7}{x+3}>0\\x+3\ne0\end{cases}}\)\(\Leftrightarrow\orbr{\begin{cases}x>\frac{-7}{5}\\x< -3\end{cases}}\)

\(\Rightarrow\left(\sqrt{\frac{5x+7}{x+3}}\right)^2=4^2\)

\(\Leftrightarrow\frac{5x+7}{x+3}=16\)

\(\Leftrightarrow5x+7=16\left(x+3\right)\)

\(\Leftrightarrow5x+7=16x+48\)

\(\Leftrightarrow-11x=41\)

\(\Leftrightarrow x=\frac{-41}{11}\)(tm)

Vậy phương trình có 1 nghiệm duy nhất là \(x=\frac{-41}{11}\)

\(\frac{y+5}{y^2-5y}-\frac{y-5}{2y^2+10y}=\frac{y+25}{2y^2-50}\)        \(ĐKXĐ:y\ne0;y\ne5\)

\(\Leftrightarrow\frac{y+5}{y\left(y-5\right)}-\frac{y-5}{2y\left(y+5\right)}-\frac{y+25}{2\left(y^2-25\right)}=0\)

\(\Leftrightarrow\frac{2\left(y+5\right)^2-\left(y-5\right)^2}{2y\left(y-5\right)\left(y+5\right)}-\frac{y\left(y+25\right)}{2y\left(y-5\right)\left(y+5\right)}=0\)

\(\Leftrightarrow\frac{2\left(y^2+10y+25\right)-y^2+10y-25-y^2-25y}{2y\left(y-5\right)\left(y+5\right)}=0\)

\(\Leftrightarrow2y^2+20y+50-y^2+10y-25-y^2-25y=0\)

\(\Leftrightarrow5y+25=0\)

\(\Leftrightarrow5\left(y+5\right)=0\)

\(\Leftrightarrow y=-5\left(tm\right)\)

\(\)Vậy phương trình có nghiệm y=-5