Tìm MinA: \(\sqrt{x-2\sqrt{x-1}}+\sqrt{x+2\sqrt{x-1}}\)
Help meee pls :<<
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KC
2
7 tháng 11 2017
A= \(\sqrt{x-1-2\sqrt{x-1}+1}+\sqrt{x-1+2\sqrt{x-1}+1}\)
=\(\sqrt{\left(\sqrt{x-1}-1\right)^2}+\sqrt{\left(\sqrt{x-1}+1\right)^2}\)
=\(\left|\sqrt{x-1}-1\right|+\left|\sqrt{x-1}+1\right|\)
\(=\left|1-\sqrt{x-1}\right|+\left|\sqrt{x-1}+1\right|\)
\(\ge\left|\sqrt{x-1}+1+1-\sqrt{x-1}\right|\)
=2.
dấu = khi và chỉ khi \(\left(\sqrt{x-1}+1\right).\left(1-\sqrt{x-1}\right)=0\)
23 tháng 3 2021
\(=\lim\limits_{x\rightarrow+\infty}\dfrac{\sqrt{4+\dfrac{1}{x^2}}-\sqrt{\dfrac{1}{x}+\dfrac{5}{x^2}}}{2-\dfrac{7}{x}}=1\)
T
11 tháng 8 2017
ĐK: \(x\ge1\)
\(A=\sqrt{\left(x-1\right)-2\sqrt{x-1}+1}+\sqrt{\left(x-1\right)+2\sqrt{x-1}+1}\)
\(=\sqrt{\left(\sqrt{x-1}-1\right)^2}+\sqrt{\left(\sqrt{x-1}+1\right)^2}\)
\(=\left|1-\sqrt{x-1}\right|+\left|\sqrt{x-1}+1\right|\)
\(\ge\left|1-\sqrt{x-1}+\sqrt{x-1}+1\right|=2\)
Đẳng thức xảy ra \(\Leftrightarrow\left(1-\sqrt{x-1}\right)\left(\sqrt{x-1}+1\right)\ge0\)
\(\Leftrightarrow1\le x\le2\)
HT
31 tháng 7 2018
ĐK: x\(\ge\)2
\(E=\dfrac{\sqrt{x+2+2\sqrt{\left(x+2\right)\left(x-2\right)}+x-2}}{\sqrt{x^2-4}+x+2}\)
\(E=\dfrac{\sqrt{\left(\sqrt{x+2}+\sqrt{x-2}\right)^2}}{\sqrt{x^2-4}+x+2}\)
\(E=\dfrac{\left|\sqrt{x+2}+\sqrt{x-2}\right|}{\sqrt{x^2-4}+x+2}\)
\(E=\dfrac{\sqrt{x+2}+\sqrt{x-2}}{\left(x+2\right)+\sqrt{\left(x+2\right)\left(\sqrt{x-2}\right)}}\)
\(E=\dfrac{\sqrt{x+2}+\sqrt{x-2}}{\sqrt{x+2}\left(\sqrt{x+2}+\sqrt{x-2}\right)}\)
\(E=\dfrac{1}{\sqrt{x+2}}\)
Thế x=2(\(\sqrt{3}+1\))=\(2\sqrt{3}+2\) vào E:
=>\(E=\dfrac{1}{\sqrt{2\sqrt{3}+4}}\)
=>\(E=\dfrac{1}{\sqrt{3+2\sqrt{3}+1}}=\dfrac{1}{\sqrt{\left(\sqrt{3}+1\right)^2}}=\dfrac{1}{\sqrt{3}+1}\)
24 tháng 7 2020
ĐKXĐ : \(\left\{{}\begin{matrix}x\ne1\\x\ge0\\x\ne0\end{matrix}\right.\) => \(\left\{{}\begin{matrix}x>0\\x\ne1\end{matrix}\right.\)
Ta có : \(B=\left(\frac{1}{1-\sqrt{x}}+\frac{1}{1+\sqrt{x}}\right):\left(\frac{1}{1-\sqrt{x}}-\frac{1}{1+\sqrt{x}}\right)+\frac{1}{2\sqrt{x}}\)
=> \(B=\left(\frac{1+\sqrt{x}+1-\sqrt{x}}{\left(1-\sqrt{x}\right)\left(1+\sqrt{x}\right)}\right):\left(\frac{1+\sqrt{x}-1+\sqrt{x}}{\left(1-\sqrt{x}\right)\left(1+\sqrt{x}\right)}\right)+\frac{1}{2\sqrt{x}}\)
=> \(B=\left(\frac{2}{1-x}\right):\left(\frac{2\sqrt{x}}{1-x}\right)+\frac{1}{2\sqrt{x}}=\frac{2\left(1-x\right)}{2\sqrt{x}\left(1-x\right)}+\frac{1}{2\sqrt{x}}\)
=> \(B=\frac{1}{\sqrt{x}}+\frac{1}{2\sqrt{x}}=\frac{2}{2\sqrt{x}}+\frac{1}{2\sqrt{x}}=\frac{3}{2\sqrt{x}}\)
Vậy ....
NT
3
21 tháng 9 2020
Đặt \(\sqrt{x+1}=t\left(t\ge0\right)\Rightarrow x^2=t^2-1\)
\(pt\Leftrightarrow t^2-1+t=1\)
\(\Leftrightarrow t^2+t-2=0\)
\(\Leftrightarrow\orbr{\begin{cases}t=-2\left(loại\right)\\t=1\end{cases}}\)
Với \(t=1\Leftrightarrow\sqrt{x+1}=1\Leftrightarrow x+1=1\Leftrightarrow x=0\)
KL: \(x=0\)
PN
21 tháng 9 2020
không dùng ẩn phụ được không ạ ?
\(x^2+\sqrt{x+1}=1\left(đk:x\ge-1\right)\)\(< =>x^2+\sqrt{x+1}-1=0\)
\(< =>x^2+\frac{x+1-1}{\sqrt{x+1}+1}=0< =>x\left(x+\frac{1}{\sqrt{x+1}+1}\right)=0\)
\(< =>x=0\)và xử lí phần trong ngoặc là ok
24 tháng 5 2021
\(\left\{{}\begin{matrix}x+2y=5m-1\\-2x+y=2\end{matrix}\right.< =>\left\{{}\begin{matrix}2x+4y=10m-2\\-2x+y=2\end{matrix}\right.\)
\(< =>\left\{{}\begin{matrix}5y=10m\\-2x+y=2\end{matrix}\right.< =>\left\{{}\begin{matrix}y=2m\\x=m-1\end{matrix}\right.\)
=>\(\sqrt{x}+\sqrt{y}=\sqrt{2}\left(1\right)\)
=>\(\sqrt{m-1}+\sqrt{2m}=\sqrt{2}\) (\(m\ge1\))
\(< =>\left(\sqrt{m-1}\right)^2=|\left(\sqrt{2}-\sqrt{2m}\right)^2|\)
<=>\(m-1=\left[\sqrt{2}.\left(1-\sqrt{m}\right)\right]^2< =>m-1=|2.\left(1-\sqrt{m}\right)^2|\)
<=>\(m-1=|2\left(1-2\sqrt{m}+m\right)|=\left|2-4\sqrt{m}+2m\right|\)
với \(\left|2-4\sqrt{m}+2m\right|=2-4\sqrt{m}+2m< =>m\le1\)
ta có pt:
<=>\(m-1-2+4\sqrt{m}-2m=0\)
\(< =>-m+4\sqrt{m}-3=0< =>-\left(m-4\sqrt{m}+3\right)=0\)
<=>\(m-4\sqrt{m}+3=0< =>\left(\sqrt{m}-3\right)\left(\sqrt{m}-1\right)=0\)
<=>\(\left[{}\begin{matrix}\sqrt{m}-3=0\\\sqrt{m}-1=0\end{matrix}\right.< =>\left[{}\begin{matrix}m=9\left(loai\right)\\m=1\left(TM\right)\end{matrix}\right.\)
nếu \(|2-4\sqrt{m}+2m|=-2+4\sqrt{m}-2m< =>m\ge1\)
=>\(-2+4\sqrt{m}-2m=m-1< =>3m-4\sqrt{m}+1=0\)
<=>\(3\left(m-2.\dfrac{2}{3}\sqrt{m}+\dfrac{1}{3}\right)=3\left(m-2.\dfrac{2}{3}\sqrt{m}+\dfrac{4}{9}-\dfrac{4}{9}+\dfrac{1}{3}\right)=0\)
<=>\(\left(\sqrt{m}-1\right)\left(\sqrt{m}-\dfrac{1}{3}\right)=0\)=>\(\left[{}\begin{matrix}\sqrt{m}-1=0\\\sqrt{m}-\dfrac{1}{3}=0\end{matrix}\right.< =>\left\{{}\begin{matrix}m=1\left(TM\right)\\m=\dfrac{1}{3}\left(loai\right)\end{matrix}\right.\)
vậy m=1 thì pt đã cho có 2 nghiệm (x,y) thỏa mãn
\(\sqrt{x}+\sqrt{y}=\sqrt{2}\)
\(A=\sqrt{x-2\sqrt{x-1}}+\sqrt{x+2\sqrt{x-1}}\)
\(=\sqrt{x-1-2\sqrt{x-1}+1}+\sqrt{x-1+2\sqrt{x-1}+1}\)
\(=\sqrt{\left(\sqrt{x-1}-1\right)^2}+\sqrt{\left(\sqrt{x-1}+1\right)^2}\)
\(=\left|\sqrt{x-1}-1\right|+\left|\sqrt{x-1}+1\right|\)
\(=\left|1-\sqrt{x-1}\right|+\left|\sqrt{x-1}+1\right|\)
\(\ge\left|1-\sqrt{x-1}+\sqrt{x-1}+1\right|=2\)
Dấu "=" xảy ra \(\Leftrightarrow\left(1-\sqrt{x-1}\right)\left(\sqrt{x-1}+1\right)\ge0\Leftrightarrow0\le x\le2\)
Vậy \(A_{min}=2\) tại \(0\le x\le2\)