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MV
12 tháng 8 2017
a,
\(\sqrt{9-12x+4x^2}=4\\ \sqrt{\left(3-2x\right)^2}=4\\ \left|3-2x\right|=4\\ \Rightarrow\left[{}\begin{matrix}3-2x=4\\3-2x=-4\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}2x=-1\\2x=7\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=\dfrac{-1}{2}\\x=\dfrac{7}{2}\end{matrix}\right.\)
Vậy \(\left[{}\begin{matrix}x=\dfrac{-1}{2}\\x=\dfrac{7}{2}\end{matrix}\right.\)
CW
25 tháng 6 2018
a) \(2\sqrt{2x}-5\sqrt{8x}+7\sqrt{18x}=28\) (*)
đk: x >/ 0
(*) \(\Leftrightarrow2\sqrt{2x}-10\sqrt{2x}+21\sqrt{2x}=28\)
\(\Leftrightarrow13\sqrt{2x}=28\) \(\Leftrightarrow\sqrt{2x}=\dfrac{28}{13}\Leftrightarrow2x=\left(\dfrac{28}{13}\right)^2\Leftrightarrow x=\dfrac{392}{169}\left(N\right)\)
Kl: \(x=\dfrac{392}{169}\)
b) \(\sqrt{4x-20}+\sqrt{x-5}-\dfrac{1}{3}\sqrt{9x-45}=4\) (*)
đk: x >/ 5
(*) \(\Leftrightarrow2\sqrt{x-5}+\sqrt{x-5}-\sqrt{x-5}=4\)
\(\Leftrightarrow2\sqrt{x-5}=4\Leftrightarrow\sqrt{x-5}=2\Leftrightarrow x-5=4\Leftrightarrow x=9\left(N\right)\)
Kl: x=9
c) \(\sqrt{\dfrac{3x-2}{x+1}}=2\) (*)
Đk: \(\left[{}\begin{matrix}x< -1\\x\ge\dfrac{2}{3}\end{matrix}\right.\)
(*) \(\Leftrightarrow\dfrac{3x-2}{x+1}=4\Leftrightarrow3x-2=4x+4\Leftrightarrow x=-6\left(N\right)\)
Kl: x=-6
d) \(\dfrac{\sqrt{5x-4}}{\sqrt{x+2}}=2\) (*)
Đk: \(x\ge\dfrac{4}{5}\)
(*) \(\Leftrightarrow\sqrt{5x-4}=2\sqrt{x+2}\Leftrightarrow5x-4=4x+8\Leftrightarrow x=12\left(N\right)\)
Kl: x=12
PA
28 tháng 9 2017
a)
\(\sqrt{3x^2+6x+7}+\sqrt{5x^2+10x+21}=5-2x-x^2\)
\(\Leftrightarrow\sqrt{3\left(x+1\right)^2+4}+\sqrt{5\left(x+1\right)^2+16}=6-\left(x+1\right)^2\)
\(VT\ge6;VP\le6\Rightarrow VT=VP=6\)
Vậy pt có một nghiệm duy nhất là \(x=-1\)
b)
\(\sqrt{4x^2+20x+25}+\sqrt{x^2-8x+16}=\sqrt{x^2+18x+81}\)
\(\Leftrightarrow\sqrt{\left(2x+5\right)^2}+\sqrt{\left(x-4\right)^2}=\sqrt{\left(x+9\right)^2}\)
\(\Leftrightarrow\left|2x+5\right|+\left|x-4\right|=\left|x+9\right|\)
Lập bảng xét dấu ra nhé ~^o^~
BC
0
AY
2
AT
25 tháng 7 2018
đkxđ: x≥\(-\dfrac{1}{2}\)
\(\sqrt{18x+9}-\sqrt{8x+4}+\dfrac{1}{3}\sqrt{2x+1}=4\)
\(\Leftrightarrow3\sqrt{2x+1}-2\sqrt{2x+1}+\dfrac{1}{3}\sqrt{2x+1}=4\)
\(\Leftrightarrow\left(3-2+\dfrac{1}{3}\right)\sqrt{2x+1}=4\)
\(\Leftrightarrow\dfrac{4}{3}\sqrt{2x+1}=4\)
\(\Leftrightarrow\sqrt{2x+1}=3\Leftrightarrow2x+1=9\Leftrightarrow x=4\)
vậy x = 4
25 tháng 7 2018
Bình phương 2 vế ,ta có:
\(26x+13+\dfrac{1}{9}\left(2x+1\right)-2\sqrt{9.4\left(2x+1\right)^2}-2.\dfrac{1}{3}\sqrt{4\left(2x+1\right)^2}+2.\dfrac{1}{3}\sqrt{9\left(2x+1\right)^2}=16\) \(\dfrac{236}{9}x+\dfrac{118}{9}-2.6.\left(2x+1\right)-\dfrac{2}{3}.2.\left(2x+1\right)+\dfrac{2}{3}.3.\left(2x+1\right)=16\)
\(\dfrac{236}{9}x+\dfrac{118}{9}-24x-12-\dfrac{8}{3}x-\dfrac{4}{3}+4x+2=16\)
\(\dfrac{32}{9}x+\dfrac{16}{9}=16\)
\(\dfrac{16}{9}\left(2x+1\right)=16\)
\(2x+1=9\Rightarrow2x=8\Rightarrow x=4\)
Vậy x=4
T
1 tháng 8 2017
a) \(\sqrt{x^2-9}-\sqrt{4x-12}=0\) ĐK: \(x\ge3\)
\(\Leftrightarrow\sqrt{\left(x-3\right)\left(x+3\right)}-2\sqrt{x-3}=0\)
\(\Leftrightarrow\sqrt{x-3}\left(\sqrt{x+3}-2\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}\sqrt{x-3}=0\\\sqrt{x+3}-2=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=3\\x=1\end{matrix}\right.\)
Vậy x = 3
b) \(\sqrt{1-x}+\sqrt{x}=1\) ĐK: \(0\le x\le1\)
\(\Leftrightarrow1-x+x+2\sqrt{x\left(1-x\right)}=1\)
\(\Leftrightarrow x\left(1-x\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x=1\end{matrix}\right.\) (Nhận)
c) \(\sqrt{x+3}+\sqrt{x+8}=5\) ĐK: \(x\ge-3\)
Đặt \(\left\{{}\begin{matrix}a=\sqrt{x+3}\ge0\\b=\sqrt{x+8}\ge0\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}a+b=5\\b^2-a^2=5\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}a+b=5\\b-a=1\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}a=2\\b=3\end{matrix}\right.\)
\(\Leftrightarrow x=1\) (Nhận)
d) \(\sqrt{16-32x}-\sqrt{12x}=\sqrt{3x}+\sqrt{9-18x}\) ĐK: \(-\dfrac{1}{2}\le x\le0\)
\(\Leftrightarrow4\sqrt{1-2x}-2\sqrt{3x}=\sqrt{3x}+3\sqrt{1-2x}\)
\(\Leftrightarrow\sqrt{1-2x}=3\sqrt{3x}\)
\(\Leftrightarrow1-2x=27x\)
\(\Leftrightarrow x=\dfrac{1}{29}\) (Nhận)
PA
14 tháng 9 2017
\(\left(\sqrt{3x+4}-\sqrt{3x+2}\right)\left(\sqrt{9x^2+18x+8}+1\right)=2\)
\(\Leftrightarrow\left(\sqrt{3x+4}-\sqrt{3x+2}\right)\left(\sqrt{\left(3x+4\right)\left(3x+2\right)}+1\right)=2\)
Đặt \(\left\{{}\begin{matrix}\sqrt{3x+4}=a\\\sqrt{3x+2}=b\end{matrix}\right.\)\(\left(a,b\ge0\right)\), ta có hpt:
\(\left\{{}\begin{matrix}a^2-b^2=2\left(1\right)\\\left(a-b\right)\left(ab+1\right)=2\end{matrix}\right.\)
\(\Leftrightarrow a^2-b^2=\left(a-b\right)\left(ab+1\right)\)
\(\Leftrightarrow\left(a-b\right)\left(a+b\right)-\left(a-b\right)\left(ab+1\right)\)
\(\Leftrightarrow\left(a-b\right)\left(a+b-ab-1\right)=0\)
\(\Leftrightarrow\left(a-b\right)\left(b-1\right)\left(1-a\right)=0\)
* Trường hợp 1: \(a-b=0\Leftrightarrow a=b\)
\(\Rightarrow\sqrt{3x+4}=\sqrt{3x+2}\)
\(\Leftrightarrow0x=\sqrt{2}-2\)
=> Pt vô no
* Trường hợp 2: \(b-1=0\Leftrightarrow b=1\)
\(\Rightarrow\sqrt{3x+2}=1\)
\(\Leftrightarrow x=-\dfrac{1}{3}\left(n\right)\)
* Trường hợp 3: \(a-1=0\Leftrightarrow a=1\)
\(\Rightarrow\sqrt{3x+4}=1\)
\(\Rightarrow x=-1\left(l\right)\)
Vậy x = \(-\dfrac{1}{3}\)