\(2x^2-3x-1=\sqrt{2x^2-x-6}+\sqrt{2x^2-5x+2}\)
giải phương trình
mn help meeeee
#camon
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NM
2
25 tháng 11 2023
ĐKXĐ: \(x\in R\)
\(3x^2-5x+6=2x\cdot\sqrt{x^2-x+2}\)
=>\(3x^2-6x+x-2+8=2\cdot\sqrt{x^4-x^3+2x^2}\)
=>\(\left(x-2\right)\left(3x+1\right)=2\cdot\left(\sqrt{x^4-x^3+2x^2}-4\right)\)
\(\Leftrightarrow\left(x-2\right)\left(3x+1\right)=2\cdot\dfrac{x^4-x^3+2x^2-16}{\sqrt{x^4-x^3+2x^2}+4}\)
=>\(\left(x-2\right)\left(3x+1\right)=2\cdot\dfrac{x^4-2x^3+x^3-2x^2+4x^2-8x+8x-16}{\sqrt{x^4-x^3+2x^2}+4}\)
=>\(\left(x-2\right)\left(3x+1\right)=\dfrac{2\left(x-2\right)\left(x^3+x^2+4x+8\right)}{\sqrt{x^4-x^3+2x^2}+4}\)
=>\(\left(x-2\right)\left[\left(3x+1\right)-\dfrac{2\left(x^3+x^2+4x+8\right)}{\sqrt{x^4-x^3+2x^2}+4}\right]=0\)
=>x-2=0
=>x=2(nhận)
25 tháng 11 2023
\(3x^2-5x+6=2x\sqrt{x^2-x+2}\)
\(\Leftrightarrow\left[x^2-2x\sqrt{x^2-x+2}+\left(x^2-x+2\right)\right]+\left(x^2-4x+4\right)=0\)
\(\Leftrightarrow\left(x-\sqrt{x^2-x+2}\right)^2+\left(x-2\right)^2=0\)
\(\Leftrightarrow\left\{{}\begin{matrix}x=\sqrt{x^2-x+2}\\x-2=0\end{matrix}\right.\Leftrightarrow x=2\)
Thử lại ta thấy nghiệm \(x=2\) thỏa phương trình ban đầu.
25 tháng 11 2021
\(a,PT\Leftrightarrow\left|x+3\right|=3x-6\\ \Leftrightarrow\left[{}\begin{matrix}x+3=3x-6\left(x\ge-3\right)\\x+3=6-3x\left(x< -3\right)\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{9}{2}\left(tm\right)\\x=\dfrac{3}{4}\left(ktm\right)\end{matrix}\right.\\ \Leftrightarrow x=\dfrac{9}{2}\\ b,PT\Leftrightarrow\left|x-1\right|=\left|2x-1\right|\\ \Leftrightarrow\left[{}\begin{matrix}x-1=2x-1\\1-x=2x-1\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\x=\dfrac{2}{3}\end{matrix}\right.\)
\(c,ĐK:x\le\dfrac{2}{5}\\ PT\Leftrightarrow4-5x=25x^2-20x+4\\ \Leftrightarrow25x^2-15x=0\\ \Leftrightarrow5x\left(5x-3\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=0\left(tm\right)\\x=\dfrac{3}{5}\left(ktm\right)\end{matrix}\right.\Leftrightarrow x=0\\ d,ĐK:x\le\dfrac{2}{5}\\ PT\Leftrightarrow4-5x=2-5x\\ \Leftrightarrow x\in\varnothing\)
NV
Nguyễn Việt Lâm
Giáo viên
20 tháng 8 2021
a.
ĐKXĐ: \(x^2+2x-1\ge0\)
\(x^2+2x-1+2\left(x-1\right)\sqrt{x^2+2x-1}-4x=0\)
Đặt \(\sqrt{x^2+2x-1}=t\ge0\)
\(\Rightarrow t^2+2\left(x-1\right)t-4x=0\)
\(\Delta'=\left(x-1\right)^2+4x=\left(x+1\right)^2\)
\(\Rightarrow\left[{}\begin{matrix}t=1-x+x+1=2\\t=1-x-x-1=-2x\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}\sqrt{x^2+2x-1}=2\\\sqrt{x^2+2x-1}=-2x\left(x\le0\right)\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x^2+2x-5=0\\3x^2-2x+1=0\left(vn\right)\end{matrix}\right.\)
\(\Rightarrow x=-1\pm\sqrt{6}\)
NV
Nguyễn Việt Lâm
Giáo viên
20 tháng 8 2021
b.
ĐKXĐ: \(x\ge\dfrac{1}{5}\)
\(2x^2+x-3+2x-\sqrt{5x-1}+2-\sqrt[3]{9-x}=0\)
\(\Leftrightarrow\left(x-1\right)\left(2x+3\right)+\dfrac{\left(x-1\right)\left(4x-1\right)}{2x+\sqrt[]{5x-1}}+\dfrac{x-1}{4+2\sqrt[3]{9-x}+\sqrt[3]{\left(9-x\right)^2}}=0\)
\(\Leftrightarrow\left(x-1\right)\left(2x+3+\dfrac{4x-1}{2x+\sqrt[]{5x-1}}+\dfrac{1}{4+2\sqrt[3]{9-x}+\sqrt[3]{\left(9-x\right)^2}}\right)=0\)
\(\Leftrightarrow x=1\) (ngoặc đằng sau luôn dương)
NV
Nguyễn Việt Lâm
Giáo viên
22 tháng 3 2021
a. ĐKXĐ: \(x\ge\dfrac{1}{2}\)
Đặt \(\left\{{}\begin{matrix}\sqrt{x^2+2x}=a>0\\\sqrt{2x-1}=b\ge0\end{matrix}\right.\)
\(\Rightarrow a+b=\sqrt{3a^2-b^2}\)
\(\Leftrightarrow\left(a+b\right)^2=3a^2-b^2\)
\(\Leftrightarrow a^2-ab-b^2=0\Leftrightarrow\left(a-\dfrac{1+\sqrt{5}}{2}b\right)\left(a+\dfrac{\sqrt{5}-1}{2}b\right)=0\)
\(\Leftrightarrow a=\dfrac{1+\sqrt{5}}{2}b\Leftrightarrow\sqrt{x^2+2x}=\dfrac{1+\sqrt{5}}{2}\sqrt{2x-1}\)
\(\Leftrightarrow x^2+2x=\dfrac{3+\sqrt{5}}{2}\left(2x-1\right)\)
\(\Leftrightarrow x^2-\left(\sqrt{5}+1\right)x+\dfrac{3+\sqrt{5}}{2}=0\)
\(\Leftrightarrow\left(x-\dfrac{\sqrt{5}+1}{2}\right)^2=0\)
\(\Leftrightarrow x=\dfrac{\sqrt{5}+1}{2}\)
NV
Nguyễn Việt Lâm
Giáo viên
22 tháng 3 2021
b. ĐKXĐ: \(x\ge5\)
\(\Leftrightarrow\sqrt{5x^2+14x+9}=\sqrt{x^2-x-20}+5\sqrt{x+1}\)
\(\Leftrightarrow5x^2+14x+9=x^2-x-20+25\left(x+1\right)+10\sqrt{\left(x+1\right)\left(x-5\right)\left(x+4\right)}\)
\(\Leftrightarrow2x^2-5x+2=5\sqrt{\left(x^2-4x-5\right)\left(x+4\right)}\)
Đặt \(\left\{{}\begin{matrix}\sqrt{x^2-4x-5}=a\ge0\\\sqrt{x+4}=b>0\end{matrix}\right.\)
\(\Rightarrow2a^2+3b^2=5ab\)
\(\Leftrightarrow\left(a-b\right)\left(2a-3b\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}\sqrt{x^2-4x-5}=\sqrt{x+4}\\2\sqrt{x^2-4x-5}=3\sqrt{x+4}\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x^2-4x-5=x+4\\4\left(x^2-4x-5\right)=9\left(x+4\right)\end{matrix}\right.\)
\(\Leftrightarrow...\)
OP
1
NV
Nguyễn Việt Lâm
Giáo viên
22 tháng 1 2022
Đặt \(\left\{{}\begin{matrix}\sqrt{2x^2+5x+12}=a>0\\\sqrt{2x^2+3x+2}=b>0\end{matrix}\right.\) \(\Rightarrow x+5=\dfrac{a^2-b^2}{2}\)
Phương trình trở thành:
\(a+b=\dfrac{a^2-b^2}{2}\)
\(\Leftrightarrow\left(a-b-2\right)\left(a+b\right)=0\)
\(\Leftrightarrow a-b-2=0\) (do \(a+b>0\))
\(\Leftrightarrow a=b+2\)
\(\Leftrightarrow\sqrt{2x^2+5x+12}=\sqrt{2x^2+3x+2}+2\)
\(\Leftrightarrow2x^2+5x+12=2x^2+3x+6+4\sqrt{2x^2+3x+2}\)
\(\Leftrightarrow x+3=2\sqrt{2x^2+3x+2}\) (\(x\ge-3\))
\(\Leftrightarrow x^2+6x+9=4\left(2x^2+3x+2\right)\)
\(\Leftrightarrow7x^2+6x-1=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-1\\x=\dfrac{1}{7}\end{matrix}\right.\)
NA
1
NV
Nguyễn Việt Lâm
Giáo viên
30 tháng 7 2021
ĐKXĐ: \(x\ge\dfrac{1}{5}\)
\(\Leftrightarrow\sqrt{3x+5}-\sqrt{2x+6}+\sqrt{5x-1}-2=0\)
\(\Leftrightarrow\dfrac{x-1}{\sqrt{3x+5}+\sqrt{2x+6}}+\dfrac{5\left(x-1\right)}{\sqrt{5x-1}+2}=0\)
\(\Leftrightarrow\left(x-1\right)\left(\dfrac{1}{\sqrt{3x+5}+\sqrt{2x+6}}+\dfrac{5}{\sqrt{5x-1}+2}\right)=0\)
\(\Leftrightarrow x-1=0\)
\(\Leftrightarrow x=1\)
18 tháng 5 2021
b)đk:\(x\ge\dfrac{1}{2}\)
Có: \(\sqrt{2x^2-1}\le\dfrac{2x^2-1+1}{2}=x^2\)
\(x\sqrt{2x-1}=\sqrt{\left(2x^2-x\right)x}\le\dfrac{2x^2-x+x}{2}=x^2\)
=>\(\sqrt{2x^2-1}+x\sqrt{2x-1}\le2x^2\)
Dấu = xảy ra\(\Leftrightarrow x=1\)
Vậy....
c) đk: \(x\ge0\)
\(\Leftrightarrow\sqrt{x}=\sqrt{x+9}-\dfrac{2\sqrt{2}}{\sqrt{x+1}}\)
\(\Rightarrow x=x+9+\dfrac{8}{x+1}-4\sqrt{\dfrac{2\left(x+9\right)}{x+1}}\)
\(\Leftrightarrow0=9+\dfrac{8}{x+1}-4\sqrt{\dfrac{2\left(x+9\right)}{x+1}}\)
Đặt \(a=\sqrt{\dfrac{2\left(x+9\right)}{x+1}}\left(a>0\right)\)
\(\Leftrightarrow\dfrac{a^2-2}{2}=\dfrac{8}{x+1}\)
pttt \(9+\dfrac{a^2-2}{2}-4a=0\) \(\Leftrightarrow a=4\) (TM)
\(\Rightarrow4=\sqrt{\dfrac{2\left(x+9\right)}{x+1}}\) \(\Leftrightarrow16=\dfrac{2\left(x+9\right)}{x+1}\) \(\Leftrightarrow x=\dfrac{1}{7}\) (TM)
Vậy ...
18 tháng 5 2021
a)ĐKXĐ: x≥-1/3; x≤6
<=>\(\dfrac{3x-15}{\sqrt{3x+1}+4}+\dfrac{x-5}{\sqrt{x-6}+1}+\left(x-5\right)\cdot\left(3x+1\right)=0\Leftrightarrow\left(x-5\right)\cdot\left(\dfrac{3}{\sqrt{3x+1}+4}+\dfrac{1}{\sqrt{x-6}+1}+3x+1\right)=0\Leftrightarrow x-5=0\Leftrightarrow x=5\)(nhận)
(vì x≥-1/3 nên3x+1≥0 )
Lời giải:
Điều kiện: \(x\geq 2\)
Ta có:
\(2x^2-3x-1=\sqrt{2x^2-x-6}+\sqrt{2x^2-5x+2}\)
Đặt \(\sqrt{2x^2-x-6}=a, \sqrt{2x^2-5x+2}=b(a,b\geq 0)\)
Khi đó. PT tương đương với:
\(\frac{a^2+b^2}{2}+1=a+b\)
\(\Leftrightarrow a^2+b^2+2-2a-2b=0\)
\(\Leftrightarrow (a-1)^2+(b-1)^2=0(*)\)
Mà \((a-1)^2, (b-1)^2\geq 0, \forall a,b\in\mathbb{R}^+\) nên $(*)$ xảy ra khi
\(\left\{\begin{matrix} (a-1)^2=0\\ (b-1)^2=0\end{matrix}\right.\Rightarrow 2x^2-x-6=2x^2-5x+2=1\)
Giải pt trên thấy vô lý, do đó pt đã cho vô nghiệm.