Giải phương trình và bất phương trình sau
a)\(\sqrt{5x}=\sqrt{35}\)
b) \(\sqrt{36\left(x-5\right)}=18\)
c)\(\sqrt{16\left(1-4x+4x^2\right)}-20=0\)
d) \(\sqrt{3-2x}\le\sqrt{5}\)
K
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NV
Nguyễn Việt Lâm
Giáo viên
16 tháng 4 2022
a.
\(3\sqrt{-x^2+x+6}\ge2\left(1-2x\right)\)
\(\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}-x^2+x+6\ge0\\1-2x< 0\end{matrix}\right.\\\left\{{}\begin{matrix}1-2x\ge0\\9\left(-x^2+x+6\right)\ge4\left(1-2x\right)^2\end{matrix}\right.\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}-2\le x\le3\\x>\dfrac{1}{2}\end{matrix}\right.\\\left\{{}\begin{matrix}x\le\dfrac{1}{2}\\25\left(x^2-x-2\right)\le0\end{matrix}\right.\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}\dfrac{1}{2}< x\le3\\\left\{{}\begin{matrix}x\le\dfrac{1}{2}\\-1\le x\le2\end{matrix}\right.\end{matrix}\right.\)
\(\Rightarrow-1\le x\le3\)
NV
Nguyễn Việt Lâm
Giáo viên
16 tháng 4 2022
b.
ĐKXĐ: \(x\ge0\)
\(\Leftrightarrow\sqrt{2x^2+8x+5}-4\sqrt{x}+\sqrt{2x^2-4x+5}-2\sqrt{x}=0\)
\(\Leftrightarrow\dfrac{2x^2+8x+5-16x}{\sqrt{2x^2+8x+5}+4\sqrt{x}}+\dfrac{2x^2-4x+5-4x}{\sqrt{2x^2-4x+5}+2\sqrt{x}}=0\)
\(\Leftrightarrow\dfrac{2x^2-8x+5}{\sqrt{2x^2+8x+5}+4\sqrt{x}}+\dfrac{2x^2-8x+5}{\sqrt{2x^2-4x+5}+2\sqrt{x}}=0\)
\(\Leftrightarrow\left(2x^2-8x+5\right)\left(\dfrac{1}{\sqrt{2x^2+8x+5}+4\sqrt{x}}+\dfrac{1}{\sqrt{2x^2-4x+5}+2\sqrt{x}}\right)=0\)
\(\Leftrightarrow2x^2-8x+5=0\)
\(\Leftrightarrow x=\dfrac{4\pm\sqrt{6}}{2}\)
30 tháng 8 2021
a: Ta có: \(\sqrt{4x+20}-3\sqrt{x+5}+\dfrac{4}{3}\sqrt{9x+45}=6\)
\(\Leftrightarrow2\sqrt{x+5}-3\sqrt{x+5}+4\sqrt{x+5}=6\)
\(\Leftrightarrow3\sqrt{x+5}=6\)
\(\Leftrightarrow x+5=4\)
hay x=-1
b: Ta có: \(\dfrac{1}{2}\sqrt{x-1}-\dfrac{3}{2}\sqrt{9x-9}+24\sqrt{\dfrac{x-1}{64}}=-17\)
\(\Leftrightarrow\dfrac{1}{2}\sqrt{x-1}-\dfrac{9}{2}\sqrt{x-1}+3\sqrt{x-1}=-17\)
\(\Leftrightarrow\sqrt{x-1}=17\)
\(\Leftrightarrow x-1=289\)
hay x=290
AH
Akai Haruma
Giáo viên
1 tháng 3 2021
Lời giải:
a) ĐK: $x\geq 0$
BPT $\Leftrightarrow \sqrt{x+2}(\sqrt{2}-1)\leq \sqrt{x}$
$\Leftrightarrow (3-2\sqrt{2})(x+2)\leq x$
$\Leftrightarrow x(2-2\sqrt{2})\leq 2(2\sqrt{2}-3)$
$\Leftrightarrow x\geq \frac{2(2\sqrt{2}-3)}{2-2\sqrt{2}}=-1+\sqrt{2}$
Vậy BPT có nghiệm $x\geq -1+\sqrt{2}$
b) ĐK: $x\geq 2$ hoặc $x\leq -2$
BPT $\Leftrightarrow (x-5)\sqrt{x^2-4}-(x-5)(x+5)\leq 0$
$\Leftrightarrow (x-5)[\sqrt{x^2-4}-(x+5)]\leq 0$Ta có 2 TH:
TH1:
\(\left\{\begin{matrix} x-5\geq 0\\ \sqrt{x^2-4}-(x+5)\leq 0\end{matrix}\right.\Leftrightarrow \left\{\begin{matrix} x\geq 5\\ \sqrt{x^2-4}\leq x+5\end{matrix}\right.\)
\(\Leftrightarrow \left\{\begin{matrix} x\geq 5\\ x^2-4\leq x^2+10x+25\end{matrix}\right.\Leftrightarrow \left\{\begin{matrix} x\geq 5\\ 29\leq 10x\end{matrix}\right.\Leftrightarrow x\geq 5\)
TH2:
\(\left\{\begin{matrix} x-5\leq 0\\ \sqrt{x^2-4}-(x+5)\geq 0\end{matrix}\right.\Rightarrow \left\{\begin{matrix} x\leq 5\\ x^2-4\geq x^2+10x+25 \end{matrix}\right.\)
\(\Leftrightarrow \left\{\begin{matrix} x\leq 5\\ -29\geq 10x\end{matrix}\right.\)
\(\Leftrightarrow \left\{\begin{matrix} x\leq 5\\ x\leq \frac{-29}{10}\end{matrix}\right.\Leftrightarrow x\leq \frac{-29}{10}\)
Kết hợp đkxđ suy ra $x\geq 5$ hoặc $x\leq \frac{-29}{10}$
5 tháng 7 2021
a) Ta có: \(\sqrt{25x+75}+3\sqrt{x-2}=2\sqrt{x-2}+\sqrt{9x-18}\)
\(\Leftrightarrow5\sqrt{x+3}+3\sqrt{x-2}=2\sqrt{x-2}+3\sqrt{x-2}\)
\(\Leftrightarrow\sqrt{25x+75}=\sqrt{4x-8}\)
\(\Leftrightarrow25x-4x=-8-75\)
\(\Leftrightarrow21x=-83\)
hay \(x=-\dfrac{83}{21}\)
b) Ta có: \(\sqrt{\left(2x-1\right)^2}=4\)
\(\Leftrightarrow\left|2x-1\right|=4\)
\(\Leftrightarrow\left[{}\begin{matrix}2x-1=4\\2x-1=-4\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}2x=5\\2x=-3\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{5}{2}\\x=-\dfrac{3}{2}\end{matrix}\right.\)
c) Ta có: \(\sqrt{\left(2x+1\right)^2}=3x-5\)
\(\Leftrightarrow\left|2x+1\right|=3x-5\)
\(\Leftrightarrow\left[{}\begin{matrix}2x+1=3x-5\left(x\ge-\dfrac{1}{2}\right)\\2x+1=5-3x\left(x< \dfrac{1}{2}\right)\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}2x-3x=-5-1\\2x+3x=5-1\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=6\left(nhận\right)\\x=\dfrac{4}{5}\left(loại\right)\end{matrix}\right.\)
d) Ta có: \(\sqrt{4x-12}-14\sqrt{\dfrac{x-2}{49}}=\sqrt{9x-18}+8\)
\(\Leftrightarrow2\sqrt{x-3}-2\sqrt{x-2}=3\sqrt{x-2}+8\)
\(\Leftrightarrow2\sqrt{x-3}-5\sqrt{x-2}=8\)
\(\Leftrightarrow4\left(x-3\right)+25\left(x-2\right)-20\sqrt{x^2-5x+6}=8\)
\(\Leftrightarrow4x-12+25x-50-8=20\sqrt{\left(x-2\right)\left(x-3\right)}\)
\(\Leftrightarrow20\sqrt{\left(x-2\right)\left(x-3\right)}=29x-70\)
\(\Leftrightarrow x^2-5x+6=\dfrac{\left(29x-70\right)^2}{400}\)
\(\Leftrightarrow x^2-5x+6=\dfrac{841}{400}x^2-\dfrac{203}{20}x+\dfrac{49}{4}\)
\(\Leftrightarrow\dfrac{-441}{400}x^2+\dfrac{103}{20}x-\dfrac{25}{4}=0\)
\(\Delta=\left(\dfrac{103}{20}\right)^2-4\cdot\dfrac{-441}{400}\cdot\dfrac{-25}{4}=-\dfrac{26}{25}\)(Vô lý)
vậy: Phương trình vô nghiệm
a) \(\sqrt{5x}=\sqrt{35}\)
ĐK : x ≥ 0
Bình phương hai vế
pt ⇔ 5x = 35 ⇔ x = 7 ( tm )
b) \(\sqrt{36\left(x-5\right)}=18\)
ĐK : x ≥ 5
Bình phương hai vế
pt ⇔ 36( x - 5 ) = 324
⇔ x - 5 = 9
⇔ x = 14 ( tm )
c) \(\sqrt{16\left(1-4x+4x^2\right)}-20=0\)
⇔ \(\sqrt{4^2\left(1-2x\right)^2}=20\)
⇔ \(\sqrt{\left(4-8x\right)^2}=20\)
⇔ \(\left|4-8x\right|=20\)
⇔ \(\orbr{\begin{cases}4-8x=20\\4-8x=-20\end{cases}}\)
⇔ \(\orbr{\begin{cases}x=-2\\x=3\end{cases}}\)
d) \(\sqrt{3-2x}\le\sqrt{5}\)
ĐK : x ≤ 3/2
Bình phương hai vế
bpt ⇔ 3 - 2x ≤ 5
⇔ -2x ≤ 2
⇔ x ≥ -1
Kết hợp với ĐK => Nghiệm của bpt là -1 ≤ x ≤ 3/2
\(a,\sqrt{5x}=\sqrt{35}\left(x\ge0\right)\)
\(\Leftrightarrow5x=35\)
\(\Leftrightarrow x=7\left(tm\right)\)
vậy...
b, \(\sqrt{36\left(x-5\right)}=18\left(x\ge5\right)\)
\(\Leftrightarrow6\sqrt{x-5}=18\)
\(\Leftrightarrow\sqrt{x-5}=3\)
\(\Leftrightarrow x-5=9\)
\(\Leftrightarrow x=14\left(tm\right)\)
vậy...
c, \(\sqrt{16\left(1-4x+4x^2\right)}-20=0\)
\(\Leftrightarrow4\sqrt{\left(1-2x\right)^2}=20\)
\(\Leftrightarrow\sqrt{\left(1-2x\right)^2}=5\)
\(\Leftrightarrow\left|1-2x\right|=5\)
\(\Leftrightarrow\orbr{\begin{cases}1-2x=5\\1-2x=-5\end{cases}}\)
\(\Leftrightarrow\orbr{\begin{cases}x=-2\\x=3\end{cases}}\)
vậy....
\(d,\sqrt{3-2x}< 5\left(x< 1.5\right)\)
\(\Leftrightarrow3-2x< 25\)
\(\Leftrightarrow-2x< 22\)
\(\Leftrightarrow x>-11\)
\(\Rightarrow-11< x< 1.5\)
vạy.