\(a.x^2+\dfrac{1}{x^2}=x+\dfrac{1}{x}\) ( ĐKXĐ : \(x\ne0\) )

\(\Leftrightarrow x^2+\dfrac{1}{x^2}-x-\dfrac{1}{x}=0\Leftrightarrow\left(x^2-\dfrac{1}{x}\right)+\left(\dfrac{1}{x^2}-x\right)=0\)

\(\Leftrightarrow-x\left(\dfrac{1}{x^2}-x\right)+\left(\dfrac{1}{x^2}-x\right)=0\Leftrightarrow\left(\dfrac{1}{x^2}-x\right)\left(1-x\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}1-x=0\\\dfrac{1}{x^2}-x=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=1\\1-x^3=0\end{matrix}\right.\)

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

\(\Leftrightarrow\left[{}\begin{matrix}x=1\\x=1\end{matrix}\right.\Leftrightarrow x=1\) ( x² + x + 1 loại nhé nếu phân tích ra thì ta được \(x^2+2.x.\dfrac{1}{2}+\dfrac{1}{4}-\dfrac{1}{4}+1=\left(x+\dfrac{1}{2}\right)^2+\dfrac{3}{4}\ge\dfrac{3}{4}\forall x\in R\) )

Vậy \(S=\left\{1\right\}\)

b, \(x\left(x+1\right)\left(x+2\right)\left(x+3\right)=24\)

\(\Leftrightarrow x\left(x+3\right).\left(x+1\right)\left(x+2\right)-24=0\)

\(\Leftrightarrow\left(x^2+3x\right)\left(x^2+3x+2\right)-24=0\)

\(\Leftrightarrow\left(x^2+3x+1-1\right)\left(x^2+3x+1+1\right)-24=0\)

\(\Leftrightarrow\left(x^2+3x+1\right)-1-24=0\Leftrightarrow\left(x^2+3x+1\right)-25=0\)

\(\Leftrightarrow\left(x^2+3x+1-5\right)\left(x^2+3x+1+5\right)=0\Leftrightarrow\left(x^2+3x-4\right)\left(x^2+3x+6\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x^2+3x-4=0\\x^2+3x+6=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}\left(x-1\right)\left(x+4\right)=0\\\left(x+\dfrac{3}{2}\right)^2+\dfrac{15}{4}\ge\dfrac{15}{4}\forall x\in R\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=1\\x=-4\end{matrix}\right.\)

Vậy \(S=\left\{-4;1\right\}\)

e, \(\left(x^2+x+1\right)-2x^2-2x=5\Leftrightarrow\left(x^2+x+1\right)-2x^2-2x-2-3=0\)

\(\Leftrightarrow\left(x^2+x+1\right)-2\left(x^2+x+1\right)-3=0\)

\(\Leftrightarrow\left(x^2+x+1\right)\left(x^2+x-1\right)-3=0< =>\left(x^2+x\right)^2-4=0\) 

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

\(\Leftrightarrow x^2+x-2=0\Leftrightarrow\left(x-1\right)\left(x+2\right)=0\) ( x^2 + x + 2 loại nhé y như mấy câu trên luôn khác 0 ! )

\(\Leftrightarrow\left[{}\begin{matrix}x=1\\x=-2\end{matrix}\right.\)

Vậy \(S=\left\{-2;1\right\}\)

Chú ý:

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

\(=\left(x^2+2x+2\right)^2\)

\(x^2+\left(x+1\right)^2+\left(x^2+x\right)^2\)

\(=\left(x^2+x\right)+x^2+x^2+2x+1\)

\(=\left(x^2+x\right)^2+2x^2+2x+1\)

\(=\left(x^2+x\right)^2+2\left(x^2+x\right)+1\)

\(=\left(x^2+x+1\right)^2\)

èo =))

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

\(\Leftrightarrow x^2\left(x-1\right)^2=\left[x+\left(x-1\right)\right]^2+2\)

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

\(\Leftrightarrow x^2\left(x-1\right)^2-4x\left(x-1\right)-3=0\) (1)

Đặt \(a=x\left(x-1\right)\)

\(x\left(x-1\right)=x^2-x=\left(x-\dfrac{1}{2}\right)^2-\dfrac{1}{4}\ge-\dfrac{1}{4}\)

\(ĐK:a^2\ge2\Leftrightarrow\left|a\right|\ge\sqrt{2}\)

\(\left(1\right)\Leftrightarrow a^2-4a-3=0\)

\(\Delta=\left(-4\right)^2-4.\left(-3\right)=16+12=28>0\)

\(\Leftrightarrow\left\{{}\begin{matrix}a=\dfrac{4+\sqrt{28}}{2}=2+\sqrt{7}\left(tm\right)\\a=\dfrac{4-\sqrt{28}}{2}=2-\sqrt{7}\left(ktm\right)\end{matrix}\right.\)

\(\rightarrow x\left(x-1\right)=2+\sqrt{7}\)

\(\Leftrightarrow x^2-x-\left(2+\sqrt{7}\right)=0\)

\(\Leftrightarrow x=\dfrac{1\pm\sqrt{9+4\sqrt{7}}}{2}\)

Vậy \(S=\left\{\dfrac{1\pm\sqrt{9+4\sqrt{7}}}{2}\right\}\)

mong mọi người giải giúp em vs 

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

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

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

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

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

\(\Leftrightarrow\left(x^2+2x-2\right)\left[\left(x-\dfrac{1}{2}\right)^2+\dfrac{3}{4}\right]=0\)

\(\Leftrightarrow x^2+2x-2=0\) (bấm máy)

\(\left(x^2+3x+3\right)^3+\left(x^2-x-1\right)^3=1^3+\left(2x^2+2x+1\right)^3\)

dùng hđt \(a^3+b^3=\left(a+b\right)\left(a^2-ab+b^2\right)\)

có nhân tử chung

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

\(\Leftrightarrow x^2+x+x^2-3x=4x\)

\(\Leftrightarrow2x^2-6x=0\)

\(\Leftrightarrow2x\left(x-3\right)=0\)

=>x=0(nhận) hoặc x=3(loại)

đk : x khác -1 ; 3 

\(\Rightarrow x\left(x+1\right)+x\left(x-3\right)=4x\Leftrightarrow2x^2-2x-4x=0\)

\(\Leftrightarrow2x^2-6x=0\Leftrightarrow2x\left(x-3\right)=0\Leftrightarrow x=0;x=3\left(ktm\right)\)