Đk:\(x\ne0;x\ge-\dfrac{1}{3}\)
Pt \(\Leftrightarrow12x^2-3x-1=4x\sqrt{3x+1}\)
\(\Leftrightarrow16x^2=4x^2+4x\sqrt{3x+1}+3x+1\)
\(\Leftrightarrow16x^2=\left(2x+\sqrt{3x+1}\right)^2\)
\(\Leftrightarrow\left[{}\begin{matrix}4x=2x+\sqrt{3x+1}\\4x=-\left(2x+\sqrt{3x+1}\right)\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}2x=\sqrt{3x+1}\left(1\right)\\6x=-\sqrt{3x+1}\left(2\right)\end{matrix}\right.\)
TH1 \(\Leftrightarrow\left\{{}\begin{matrix}x\ge0\\4x^2=3x+1\end{matrix}\right.\)\(\Leftrightarrow\left\{{}\begin{matrix}x\ge0\\\left(x-1\right)\left(4x+1\right)=0\end{matrix}\right.\)\(\Rightarrow x=1\) (thỏa)
TH2\(\Leftrightarrow\left\{{}\begin{matrix}x\le0\\36x^2=3x+1\end{matrix}\right.\)\(\Leftrightarrow\left\{{}\begin{matrix}x\le0\\\left[{}\begin{matrix}x=\dfrac{1+\sqrt{17}}{24}\\x=\dfrac{1-\sqrt{17}}{24}\end{matrix}\right.\end{matrix}\right.\)\(\Rightarrow x=\dfrac{1-\sqrt{17}}{24}\)(tm)
Vậy...
Lời giải:
ĐKXĐ: $x\ge \frac{-1}{3}; x\neq 0$
PT \(\Leftrightarrow 3(x-1)+\frac{x-1}{4x}=\sqrt{3x+1}-2\)
\(\Leftrightarrow 3(x-1)+\frac{x-1}{4x}=\frac{3(x-1)}{\sqrt{3x+1}+2}\)
\(\Leftrightarrow (x-1)(3+\frac{1}{4x}-\frac{3}{\sqrt{3x+1}+2})=0\)
Nếu $x-1=0\Leftrightarrow x=1$ (tm)
Nếu $3+\frac{1}{4x}-\frac{3}{\sqrt{3x+1}+2}=0$
$\Leftrightarrow 12x\sqrt{3x+1}+12x+\sqrt{3x+1}+2=0$
$\Leftrightarrow \sqrt{3x+1}(12x+1)=-(12x+2)$
Từ đây suy ra $x\leq \frac{-1}{6}$
Bình phương 2 vế:
$(3x+1)(12x+1)^2=[(12x+1)+1]^2$
$\Leftrightarrow 3x(12x+1)^2=2(12x+1)+1$
$\Leftrightarrow 144x^3+24x^2-7x-1=0$
$\Leftrightarrow (4x+1)(36x^2-3x-1)=0$
Vì $x\leq \frac{-1}{6}$ nên $x=\frac{1-\sqrt{17}}{24}$
Cách 2:
ĐKXĐ:...........
PT $\Leftrightarrow 12x^2-3x-1=4x\sqrt{3x+1}$
$\Leftrightarrow \frac{3}{4}(4x)^2-(3x+1)=4x\sqrt{3x+1}$
Đặt $4x=a; \sqrt{3x+1}=b$ thì pt trở thành:
$\frac{3}{4}a^2-b^2=ab$
$\Leftrightarrow 3a^2-4b^2-4ab=0$
$\Leftrightarrow (a-2b)(3a+2b)=0$
Nếu $a-2b=0\Leftrightarrow 4x=2\sqrt{3x+1}$
$\Rightarrow 4x^2=3x+1$ và $x\geq 0$
$\Rightarrow x=1$ (chọn) hoặc $x=-\frac{1}{4}$ (loại do $x\geq 0$)
Nếu $3a+2b=0$
$\Leftrightarrow 12x=-2\sqrt{3x+1}$
Bình phương lên ta cũng thu được $x=\frac{1-\sqrt{17}}{24}$
