C=\(\text{|}x-x+1\text{|}+\text{|}x^2-x+2\text{|}\)
tim GTNN
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22 tháng 9 2023 lúc 22:21
Tìm GTNN của biểu thức sau :
\(\sqrt{\text{x-1}\text{-2}\sqrt{\text{x-2}}}-\sqrt{\text{x+7}\text{-6}\sqrt{\text{x-2}}}\)
Ta có: \(A=\sqrt{x-1-2\sqrt{x-2}}-\sqrt{x+7-6\sqrt{x-2}}\)
\(=\sqrt{x-2-2\cdot\sqrt{x-2}\cdot1+1}-\sqrt{x-2-6\cdot\sqrt{x-2}+9}\)
\(=\sqrt{\left(\sqrt{x-2}-1\right)^2}-\sqrt{\left(\sqrt{x-2}-3\right)^2}=\left|\sqrt{x-2}-1\right|-\left|\sqrt{x-2}-3\right|\)
=>\(A\le\left|\sqrt{x-2}-1-\sqrt{x-2}+3\right|=2\forall x\) thỏa mãn ĐKXĐ
Dấu '=' xảy ra khi \(\left(\sqrt{x-2}-1\right)\left(\sqrt{x-2}-3\right)\ge0\)
=>\(\left[\begin{array}{l}\sqrt{x-2}\ge3\\ \sqrt{x-2}\le1\end{array}\right.\Rightarrow\left[\begin{array}{l}x-2\ge9\\ 0\le x-2\le1\end{array}\right.\Rightarrow\left[\begin{array}{l}x\ge11\\ 2\le x\le3\end{array}\right.\)
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Tìm GTNN
\(\sqrt{\text{x}+1}+\sqrt{\text{x}-1}+2\sqrt{\text{x}}\)
ban oi bai nay la bai cua de thi vao lop 10 hanoi nam 2018-2019 :
http://kenh14.vn/dap-an-de-thi-mon-toan-tuyen-sinh-vao-lop-10-tai-ha-noi-nam-hoc-2018-2019-20180607165723991.chn
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Thực hiện phép tínha) frac{text{x + 9}}{x^2 - 9}-frac{text{3}}{text{x^2 + 3x}}b) frac{text{3x + 5
}}{text{x^2 - 5x
}}+frac{text{ 25 - x
}}{text{25 - 5x
}}c) frac{text{3
}}{text{2x
}}+frac{text{3x - 3
}}{text{2x - 1
}}+frac{ 2x^2 + 1
}{text{4x^2 - 2x
}}d) frac{text{1}}{text{3x - 2 }}-frac{1}{text{3x + 2 }}- frac{text{3x - 6}}{text{4 - 9x^2}}e) frac{text{18 }}{text{(x - 3)(x^2 - 9) }}-frac{text{3 }}{text{x^2 - 6x + 9 }}-frac{text{x}}{text{x^2 - 9}}g) frac{text{x + 2 }}{text{x + 3 }}-frac{text{...
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Thực hiện phép tính
a) \(\frac{\text{x + 9}}{x^2 - 9}-\frac{\text{3}}{\text{x^2 + 3x}}\)
b) \(\frac{\text{3x + 5 }}{\text{x^2 - 5x }}+\frac{\text{ 25 - x }}{\text{25 - 5x }}\)
c) \(\frac{\text{3 }}{\text{2x }}+\frac{\text{3x - 3 }}{\text{2x - 1 }}+\frac{ 2x^2 + 1 }{\text{4x^2 - 2x }}\)
d) \(\frac{\text{1}}{\text{3x - 2 }}-\frac{1}{\text{3x + 2 }}- \frac{\text{3x - 6}}{\text{4 - 9x^2}}\)
e) \(\frac{\text{18 }}{\text{(x - 3)(x^2 - 9) }}-\frac{\text{3 }}{\text{x^2 - 6x + 9 }}-\frac{\text{x}}{\text{x^2 - 9}}\)
g) \(\frac{\text{x + 2 }}{\text{x + 3 }}-\frac{\text{5 }}{\text{x^2 + x - 6 }}+\frac{\text{1}}{\text{2 - x}}\)
h) \(\frac{\text{4x }}{\text{x + 2 }}-\frac{\text{3x }}{\text{x - 2 }}+\frac{\text{12x}}{\text{x^2 - 4}}\)
i) \(\frac{\text{ x + 1 }}{\text{ x - 1 }}-\frac{\text{ x - 1 }}{\text{ x + 1 }}-\frac{\text{4}}{\text{1 - x^2}}\)
k) \(\frac{\text{
3x + 21
}}{\text{
x^2 - 9
}}+\frac{\text{2 }}{\text{x + 3 }}-\frac{\text{3}}{\text{x - 3}}\)
21 tháng 11 2015 lúc 9:47
\(\text{Tìm GTNN của : }A=\frac{1}{x^2+y^2}+\frac{2}{xy}+4xy\text{ với }x;y>0\text{ và }x+y<1\)
9 tháng 2 2022 lúc 20:49
Tìm GTLN GTNN của A=\(\dfrac{\text{ 2x+1}}{\text{x^2+2 }}\)
\(A=\dfrac{2x+1}{x^2+2}\)
\(\Leftrightarrow Ax^{2\:}+2A=2x+1\)
+) \(A=0\Rightarrow x=-\dfrac{1}{2}\)
+) \(A\ne0\)
\(Ax^2+2A=2x+1\)
\(\Leftrightarrow Ax^{2\:}-2x=1-2A\)
\(\Leftrightarrow x^2-2.\dfrac{x}{A}=\dfrac{1-2A}{A}\)
\(\Leftrightarrow x^2-2.x.\dfrac{1}{A}+\dfrac{1}{A^2}=\dfrac{1-2A}{A}+\dfrac{1}{A^2}\)
\(\Leftrightarrow\left(x-\dfrac{1}{A}\right)^2=\dfrac{A-2A^2+1}{A^2}\)
\(\Leftrightarrow\left(x-\dfrac{1}{A}\right)^2=\dfrac{\left(1-A\right)\left(2A+1\right)}{A^2}\)
Vì \(\left\{{}\begin{matrix}\left(x-\dfrac{1}{A}\right)^2\ge0\left(\forall x,A\ne0\right)\\A^2\ge0\end{matrix}\right.\)
⇒ \(\left(1-A\right)\left(2A+1\right)\ge0\)
⇒ \(-\dfrac{1}{2}\le A\le1\)
Còn lại tụ làm nha
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\(A=\dfrac{2x+1}{x^2+2}=\dfrac{x^2+2-x^2-2+2x+1}{x^2+2}\\ =1-\dfrac{-\left(x-1\right)^2}{x^2+2}\\ Do\left(x-1\right)^2\ge0\Rightarrow\dfrac{-\left(x-1\right)^2}{x^2+2}\ge0\\ \Rightarrow\dfrac{-\left(x-1\right)^2}{x^2+2}=0\Leftrightarrow\dfrac{-\left(x-1\right)^2}{x^2+2}+1\le1\)
\(Dấu"="\Leftrightarrow A=1\\ \Leftrightarrow x-1=0\Rightarrow x=1\\ Vậy.P_{max}=1.khi.x=1\\ A=\dfrac{2x+1}{x^2+2}\rightarrow2A+1=\dfrac{2.\left(2x+1\right)}{x^2+2}+1\\ =\dfrac{4x+2+x^2+2}{x^2+2}=\dfrac{x^2+4x+2}{x^2+2}=\dfrac{\left(x+2\right)^2}{x^2+2}\\ Do\left(x+2\right)^2\ge0\Leftrightarrow\dfrac{\left(x+2\right)^2}{x^2+2}\ge0\)
\(Dấu"="\Leftrightarrow A=\dfrac{1}{2}khi.x=-2\\ \Rightarrow2A+1\ge0\Rightarrow2A\ge-1\Rightarrow A>-\dfrac{1}{2}\\ Vậy.MinA=-\dfrac{1}{2}.khi.x=-2\)
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Rút gọn biểu thức C = \(\dfrac{\text{x}-\dfrac{\text{1}}{\text{x}^{\text{2}}}}{\text{1}+\dfrac{1}{x}+\dfrac{1}{x^2}}\)
Rút gọn biểu thức C = \(\dfrac{\text{x}-\dfrac{\text{1}}{\text{x}^{\text{2}}}}{\text{1}+\dfrac{1}{x}+\dfrac{1}{x^2}}\)
\(C=\dfrac{x-\dfrac{1}{x^2}}{1+\dfrac{1}{x}+\dfrac{1}{x^2}}\)
Đk: \(x\ne0\)
\(\Rightarrow C=\dfrac{\dfrac{x^3-1}{x^2}}{\dfrac{x^2+x+1}{x^2}}=\dfrac{x^3-1}{x^2+x+1}\)
\(=\dfrac{\left(x-1\right)\left(x^2+x+1\right)}{x^2+x+1}=x-1\)
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\(=\dfrac{\dfrac{x^3-1}{x^2}}{\dfrac{x^2+x+1}{x^2}}=\dfrac{\left(x-1\right)\left(x^2+x+1\right)}{x^2+x+1}=x-1\)
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22 tháng 11 2021 lúc 19:44
C=\(\left(\dfrac{1}{1-x}+\dfrac{2}{x+1}-\dfrac{\text{5-x}}{\text{1-x}^{\text{2}}}\right)\):\(\dfrac{1-2x}{\text{x}^{\text{2}}-1}\)
a) Rút gọn
\(C=\dfrac{-\left(x+1\right)+2\left(x-1\right)+5-x}{\left(x-1\right)\left(x+1\right)}.\dfrac{\left(x-1\right)\left(x+1\right)}{1-2x}\)
\(=\dfrac{2}{1-2x}\)
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\(C=\left(\dfrac{1}{1-x}+\dfrac{2}{x+1}-\dfrac{5-x}{1-x^2}\right):\dfrac{1-2x}{x^2-1}\)
\(\Rightarrow C=\left(\dfrac{1+x}{\left(1-x\right)\left(1+x\right)}+\dfrac{2\left(1-x\right)}{\left(1+x\right)\left(1-x\right)}-\dfrac{5-x}{\left(1-x\right)\left(1+x\right)}\right).\dfrac{\left(x-1\right)\left(x+1\right)}{1-2x}\)
\(\Rightarrow C=\dfrac{1+x+2\left(1-x\right)-5+x}{\left(1-x\right)\left(1+x\right)}.\dfrac{\left(x-1\right)\left(x+1\right)}{1-2x}\)
\(\Rightarrow C=\dfrac{1+x+2-2x-5+x}{\left(1-x\right)\left(1+x\right)}.\dfrac{-\left(1-x\right)\left(x+1\right)}{1-2x}\)
\(\Rightarrow C=-2.\dfrac{-1}{1-2x}\)
\(\Rightarrow C=\dfrac{2}{1-2x}\)
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rút gọn các biểu thức sau
\(B=\dfrac{3\text{x}^2+6\text{x}+12}{x^3-8\dfrac{ }{ }}\)
C=\(\left(\dfrac{x+1}{2\text{x}-2}+\dfrac{3}{x^2-1}-\dfrac{x+3}{2\text{x}+2}\right).\dfrac{4\text{x}^2-4}{5}\)
E=\(\dfrac{x^2-10\text{x}+25}{x^2-5\text{x}}\)
c: \(E=\dfrac{\left(x-5\right)^2}{x\left(x-5\right)}=\dfrac{x-5}{x}\)
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