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12 tháng 7 2019
B =\(\frac{2\sqrt{x}-9}{\left(\sqrt{x}-2\right)\left(\sqrt{x}-3\right)}\) + \(\frac{2\sqrt{x}+1}{\sqrt{x}-3}\)- \(\frac{\sqrt{x}+3}{\sqrt{x}-2}\)( \(x\ge0\); \(x\ne2;3\))
= \(\frac{2\sqrt{x}-9+\left(2\sqrt{x}+1\right)\left(\sqrt{x}-2\right)-x+9}{\left(\sqrt{x}-2\right)\left(\sqrt{x}-3\right)}\)
= \(\frac{2\sqrt{x}-9+2x-3\sqrt{x}-2-x+9}{\left(\sqrt{x}-2\right)\left(\sqrt{x}-3\right)}\)
= \(\frac{x-\sqrt{x}-2}{\left(\sqrt{x}-2\right)\left(\sqrt{x}-3\right)}\)
= \(\frac{\left(\sqrt{x}-2\right)\left(\sqrt{x}+1\right)}{\left(\sqrt{x}-2\right)\left(\sqrt{x}-3\right)}\)
= \(\frac{\sqrt{x}+1}{\sqrt{x}-3}\)
b, B = \(\frac{\sqrt{x}+1}{\sqrt{x}-3}\)= \(\frac{\sqrt{x}-3+4}{\sqrt{x}-3}\)= \(1+\frac{4}{\sqrt{x}-3}\)
để B có gtri nguyên thì \(\frac{4}{\sqrt{x}-3}\)phải nguyên
\(\Rightarrow\left(\sqrt{x}-3\right)\varepsilonƯ\left(4\right)\)
\(\Rightarrow\left(\sqrt{x}-3\right)\varepsilon\left\{1;-1;2;-2;4;-4\right\}\)
ta có bảng sau
\(\sqrt{x}-3\) 1 -1 2 -2 4 -4
\(\sqrt{x}\) 4 2 5 1 7 -1 (L)
x 16 4 25 1 49
vậy x \(\varepsilon\){ 16 ; 4 ; 25; 1 ; 49 }
#mã mã#
ML
29 tháng 7 2016
a,
\(pt\Leftrightarrow\left(x-1-2\sqrt{x-1}+1\right)+\left(y-2-4\sqrt{y-2}+4\right)+\left(z-3-6\sqrt{z-3}+9\right)=0\)
\(\Leftrightarrow\left(\sqrt{x-1}-1\right)^2+\left(\sqrt{y-2}-2\right)^2+\left(\sqrt{z-3}-3\right)^2=0\)
\(\Leftrightarrow\hept{\begin{cases}\sqrt{x-1}-1=0\\\sqrt{y-2}-2=0\\\sqrt{z-3}-3=0\end{cases}}\Leftrightarrow\hept{\begin{cases}x=2\\y=6\\z=12\end{cases}}\)
20 tháng 5 2021
Câu 1:
\(A=\dfrac{2\sqrt{x}}{\sqrt{x}-3}-\dfrac{x+9\sqrt{x}}{x-9}\left(x\ge0;x\ne9\right)\)
\(=\dfrac{2\sqrt{x}\left(\sqrt{x}+3\right)}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}-\dfrac{x+9\sqrt{x}}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}\)
\(=\dfrac{2x+6\sqrt{x}-x-9\sqrt{x}}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}\)\(=\dfrac{x-3\sqrt{x}}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}=\dfrac{\sqrt{x}\left(\sqrt{x}-3\right)}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}\)\(=\dfrac{\sqrt{x}}{\sqrt{x}+3}\)
Câu 2:
\(V\left(3\right)=12000000-1400000.3=7800000\)
Có: \(V\left(t\right)=6400000\) \(\Leftrightarrow12000000-1400000t=6400000\)
\(\Leftrightarrow t=4\) => Sau 4 năm thì gtri chiếc máy tính này còn 6400000 đ
b,\(\left\{{}\begin{matrix}2x+y=5\\mx+3y=4\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}2x+\dfrac{4-mx}{3}=5\\y=\dfrac{4-mx}{3}\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}x\left(6-m\right)=11\left(1\right)\\y=\dfrac{4-mx}{3}\end{matrix}\right.\)
Xét \(m=6\) thay vào pt ta đc \(\left\{{}\begin{matrix}2x+y=5\\6x+3y=4\end{matrix}\right.\) (vô nghiệm)
\(\Rightarrow m\ne6\)
Từ (1) \(\Rightarrow x=\dfrac{11}{6-m}\)
\(\Rightarrow y=\dfrac{4-\dfrac{11m}{6-m}}{3}\)\(=\dfrac{24-15m}{3\left(6-m\right)}\)
\(xy>0\Leftrightarrow\dfrac{11}{6-m}.\dfrac{24-15m}{3\left(6-m\right)}>0\)
\(\Leftrightarrow\dfrac{11\left(24-15m\right)}{3\left(6-m\right)^2}>0\)
\(\Leftrightarrow24-15m>0\Leftrightarrow m< \dfrac{24}{15}\)
20 tháng 5 2021
`A=(2sqrtx)/(sqrtx-3)-(x+9sqrtx)/(x-9)`
`đk:x>=0,x ne 9`
`A=(2x+6sqrtx)/(x-9)-(x+9sqrtx)/(x-9)`
`=(x-3sqrtx)/(x-9)`
`=sqrtx/(sqrtx+3)`
NN
11 tháng 10 2020
a) \(ĐKXĐ:\hept{\begin{cases}x>0\\x\ne4\\x\ne9\end{cases}}\)
\(P=\left(\frac{\sqrt{x}-3}{2-\sqrt{x}}+\frac{\sqrt{x}+2}{3+\sqrt{x}}-\frac{9-x}{x+\sqrt{x}-6}\right):\left(1-\frac{3\sqrt{x}-9}{x-9}\right)\)
\(=\left[\frac{-\left(\sqrt{x}-3\right)}{\sqrt{x}-2}+\frac{\sqrt{x}+2}{\sqrt{x}+3}+\frac{x-9}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+3\right)}\right]:\left[1-\frac{3\left(\sqrt{x}-3\right)}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}\right]\)
\(=\left[\frac{-\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+3\right)}+\frac{\left(\sqrt{x}+2\right)\left(\sqrt{x}-2\right)}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+3\right)}+\frac{x-9}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+3\right)}\right]:\left(1-\frac{3}{\sqrt{x}+3}\right)\)
\(=\left[\frac{-x+9+x-4+x-9}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+3\right)}\right]:\left(\frac{\sqrt{x}+3-3}{\sqrt{x}+3}\right)\)
\(=\frac{x-4}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+3\right)}:\frac{\sqrt{x}}{\sqrt{x}+3}\)
\(=\frac{\left(\sqrt{x}-2\right)\left(\sqrt{x}+2\right)}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+3\right)}.\frac{\sqrt{x}+3}{\sqrt{x}}=\frac{\sqrt{x}+2}{\sqrt{x}}\)
b) Ta có: \(P=\frac{\sqrt{x}+2}{\sqrt{x}}=1+\frac{2}{\sqrt{x}}\)
Vì \(x\inℤ\)\(\Rightarrow\)Để P nguyên thì \(\frac{2}{\sqrt{x}}\inℤ\)
\(\Rightarrow2⋮\sqrt{x}\)\(\Rightarrow\sqrt{x}\inƯ\left(2\right)=\left\{\pm1;\pm2\right\}\)
Vì \(\sqrt{x}>0\)\(\Rightarrow\sqrt{x}\in\left\{1;2\right\}\)
\(\Rightarrow x\in\left\{1;4\right\}\)
So sánh với ĐKXĐ ta thấy \(x=1\)thỏa mãn
\(\Rightarrow P=\frac{\sqrt{1}+2}{\sqrt{1}}=\frac{1+2}{1}=3\)
Vậy \(x=1\)khi đó \(P=3\)
11 tháng 10 2020
\(P=\left(\frac{\sqrt{x}-3}{2-\sqrt{x}}+\frac{\sqrt{x}+2}{3+\sqrt{x}}-\frac{9-x}{x+\sqrt{x}-6}\right)\div\left(1-\frac{3\sqrt{x}-9}{x-9}\right)\)
a) ĐK : \(\hept{\begin{cases}x\ge0\\x\ne4\\x\ne9\end{cases}}\)
\(=\left(\frac{3-\sqrt{x}}{\sqrt{x}-2}+\frac{\sqrt{x}+2}{\sqrt{x}+3}-\frac{9-x}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+3\right)}\right)\div\left(1-\frac{3\left(\sqrt{x}-3\right)}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}\right)\)
\(=\left(\frac{\left(3-\sqrt{x}\right)\left(x+\sqrt{3}\right)}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+3\right)}+\frac{\left(\sqrt{x}+2\right)\left(\sqrt{x}-2\right)}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+3\right)}-\frac{9-x}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+3\right)}\right)\div\left(1-\frac{3}{\sqrt{x}+3}\right)\)
\(=\left(\frac{9-x}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+3\right)}+\frac{x-4}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+3\right)}-\frac{9-x}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+3\right)}\right)\div\left(\frac{\sqrt{x}+3}{\sqrt{x}+3}-\frac{3}{\sqrt{x}+3}\right)\)
\(=\left(\frac{9-x+x-4-9+x}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+3\right)}\right)\div\left(\frac{\sqrt{x}}{\sqrt{x}+3}\right)\)
\(=\frac{x-2}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+3\right)}\times\frac{\sqrt{x}+3}{\sqrt{x}}\)
\(=\frac{\left(\sqrt{x}-2\right)\left(\sqrt{x}+2\right)}{\sqrt{x}\left(\sqrt{x}-2\right)}=\frac{\sqrt{x}+2}{\sqrt{x}}\)
b) Ta có : \(\frac{\sqrt{x}+2}{\sqrt{x}}=1+\frac{2}{\sqrt{x}}\)
Để P nguyên => \(\frac{2}{\sqrt{x}}\)nguyên
=> \(2⋮\sqrt{x}\)
=> \(\sqrt{x}\inƯ\left(2\right)=\left\{\pm1;\pm2\right\}\)
=> \(\sqrt{x}\in\left\{1;2\right\}\)( vì x ≥ 0 )
=> \(x\in\left\{1;4\right\}\Rightarrow x=1\)( vì x ≠ 4 )
Vậy với x = 1 thì P có giá trị nguyên