a. Với a = -3 ta được:
\(\dfrac{x+3}{x-3}-\dfrac{x-3}{x+3}+\dfrac{27-3}{x^2-9}=0\)
\(\Leftrightarrow\dfrac{\left(x+3\right)\left(x+3\right)}{\left(x-3\right)\left(x+3\right)}-\dfrac{\left(x-3\right)\left(x-3\right)}{\left(x-3\right)\left(x+3\right)}+\dfrac{24}{\left(x-3\right)\left(x+3\right)}=0\)
\(\Leftrightarrow x^2+6x+9-x^2+6x-9+24=0\)
\(\Leftrightarrow12x+24=0\)
\(\Leftrightarrow x=-2\)
Giải phương trình :
\(\dfrac{x-a}{x+a}-\dfrac{x+a}{x-a}+\dfrac{3a^2+a}{x^2-a^2}=0\)
a) Với a = -3
\(\dfrac{x-3}{x+3}-\dfrac{x+3}{x-3}+\dfrac{27+3}{x^2-3^2}=0\)
ĐKXĐ : \(\left\{{}\begin{matrix}x+3\ne0\\x-3\ne0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x\ne-3\\x\ne3\end{matrix}\right.\)
Ta có : \(\dfrac{x-3}{x+3}-\dfrac{x+3}{x-3}+\dfrac{27+3}{x^2-3^2}\)
\(\Leftrightarrow\) \(\dfrac{\left(x-3\right)\left(x-3\right)}{\left(x+3\right)\left(x-3\right)}-\dfrac{\left(x+3\right)\left(x+3\right)}{\left(x-3\right)\left(x+3\right)}+\dfrac{27+3}{\left(x+3\right)\left(x-3\right)}=0\)
Khử mẫu ta có : \(\left(x-3\right)^2-\left(x+3\right)^2+27+3=0\)
⇔ \(x^2+6x+9-x^2+6x-9+30=0\)
\(\Leftrightarrow12x+30=0\)
\(\Leftrightarrow12x=-30\)
\(\Leftrightarrow x=-\dfrac{5}{2}\)
Tập nghiệm của pt là: \(S=\left\{-\dfrac{5}{2}\right\}\)
b) Với a = 1
\(\dfrac{x-1}{x+1}-\dfrac{x+1}{x-1}+\dfrac{3+3}{x^2-1}=0\)
ĐKXĐ : \(\left\{{}\begin{matrix}x+1\ne0\\x-1\ne0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x\ne-1\\x\ne1\end{matrix}\right.\)
Ta có : \(\dfrac{x-1}{x+1}-\dfrac{x+1}{x-1}+\dfrac{3+3}{x^2-1}=0\)
\(\Leftrightarrow\) \(\dfrac{\left(x-1\right)\left(x-1\right)}{\left(x+1\right)\left(x-1\right)}-\dfrac{\left(x+1\right)\left(x+1\right)}{\left(x-1\right)\left(x+1\right)}+\dfrac{3+3}{\left(x+1\right)\left(x-1\right)}=0\)
Khử mẫu ta có : \(\left(x-1\right)^2-\left(x+1\right)^2+6=0\)
\(\Leftrightarrow x^2+x-1-x^2+x+1+6=0\)
\(\Leftrightarrow2x+6=0\)
\(\Leftrightarrow2x=-6\)
\(\Leftrightarrow x=-3\)
Tập nghiệm của pt là : \(S=\left\{-3\right\}\)
ĐKXĐ: x khác a
b. Với a = 1 ta có pt:
\(\dfrac{x-1}{x+1}-\dfrac{x+1}{x-1}+\dfrac{3+1}{x^2-1}\)
\(\Leftrightarrow\dfrac{\left(x-1\right)\left(x-1\right)}{\left(x+1\right)\left(x-1\right)}-\dfrac{\left(x+1\right)\left(x+1\right)}{\left(x+1\right)\left(x-1\right)}+\dfrac{4}{\left(x-1\right)\left(x+1\right)}\)
\(\Leftrightarrow x^2-2x+2-x^2-2x-2+4=0\)
\(\Leftrightarrow-4x+4=0\)
\(\Leftrightarrow-4x=-4\)
\(\Leftrightarrow x=1\)( loại)
Vậy pt vô nghiệm với a = 1
