\(x\sqrt{1+y^2}+y\sqrt{1+x^2}\)
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\(y'=\dfrac{\left(x+\sqrt{x^2+1}\right)'}{2\sqrt{x+\sqrt{x^2+1}}}=\dfrac{1+\dfrac{x}{\sqrt{x^2+1}}}{2\sqrt{x+\sqrt{x^2+1}}}=\dfrac{x+\sqrt{x^2+1}}{2\sqrt{x^2+1}.\sqrt{x+\sqrt{x^2+1}}}\)
\(=\dfrac{\sqrt{x+\sqrt{x^2+1}}}{2\sqrt{x^2+1}}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a, dk \(x\ge0.x\ne1\)
\(\left(\frac{1+\sqrt{x}+1-\sqrt{x}}{2\left(1-x\right)}-\frac{x^2+1}{1-x^2}\right)\left(\frac{x+1}{x}\right)\)=\(\left(\frac{1}{1-x}-\frac{x^2+1}{1-x^2}\right)\left(\frac{x+1}{x}\right)\)
=\(\left(\frac{1+x-x^2-1}{1-x^2}\right)\left(\frac{x+1}{x}\right)=\frac{x\left(1-x\right)\left(x+1\right)}{x\left(1-x\right)\left(1+x\right)}=1\)
phan b,c ban tu lam not nhe dai lam mk ko lam dau mk co vc ban rui
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\left\{{}\begin{matrix}\sqrt{x^2+x+y+1}+x+\sqrt{y^2+x+y+1}+y=18\left(1\right)\\\sqrt{x^2+x+y+1}-x+\sqrt{y^2+x+y+1}-y=2\left(2\right)\end{matrix}\right.\)
\(\xrightarrow[\left(1\right)-\left(2\right)]{\left(1\right)+\left(2\right)}\left\{{}\begin{matrix}2\left(\sqrt{x^2+x+y+1}+\sqrt{y^2+x+y+1}\right)=20\left(3\right)\\2\left(x+y\right)=16\Rightarrow x=8-y\left(4\right)\end{matrix}\right.\)
Thay (4) vào (3) và thu gọn ta được: \(\left(\sqrt{x^2+9}+\sqrt{y^2+9}\right)=10\left(5\right)\)
Kết hợp (4) và (5): \(\left\{{}\begin{matrix}x=8-y\\\sqrt{x^2+9}+\sqrt{y^2+9}=10\end{matrix}\right.\) rồi giải nốt :D good luck
![](https://rs.olm.vn/images/avt/0.png?1311)
1. \(y'=\sqrt{x-2}+\dfrac{x+1}{2\sqrt{x-2}}\)
2. \(y'=-\dfrac{\dfrac{1}{2\sqrt{x^2+4x+5}}\cdot\left(x^2+4x+5\right)'}{x^2+4x+5}=-\dfrac{x+2}{\sqrt{\left(x^2+4x+5\right)^3}}\)
3. \(y'=\dfrac{\dfrac{x-1}{2\sqrt{x+1}}-\sqrt{x+1}}{\left(x-1\right)^2}=\dfrac{-x-3}{\left(x-1\right)^2\sqrt{x+1}}\)
4. \(y'=\dfrac{\sqrt{x^2+1}-\dfrac{x+1}{2\sqrt{x^2+1}}\cdot\left(x^2+1\right)'}{x^2+1}=\dfrac{\dfrac{2\left(x^2+1\right)-\left(x+1\right)\cdot2x}{2\sqrt{x^2+1}}}{x^2+1}=\dfrac{1-x}{\sqrt{\left(x^2+1\right)^3}}\)
5. \(y'=-\dfrac{\dfrac{\left(4-3x^2\right)'}{2\sqrt{4-3x^2}}}{4-3x^2}=\dfrac{3x}{\sqrt{\left(4-3x^2\right)^3}}\)
1. \(y'=\sqrt{x-2}+\dfrac{x+1}{2\sqrt{x-2}}=\dfrac{3x-3}{2\sqrt{x-2}}\)
2. \(y'=-\dfrac{\left(\sqrt{x^2+4x+5}\right)'}{x^2+4x+5}=-\dfrac{x+2}{\left(x^2+4x+5\right)\sqrt{x^2+4x+5}}\)
3. \(y'=\dfrac{\dfrac{\left(x-1\right)}{2\sqrt{x+1}}-\sqrt{x+1}}{\left(x-1\right)^2}=\dfrac{-x-3}{2\left(x-1\right)^2\sqrt{x+1}}\)
4. \(y'=\dfrac{\sqrt{x^2+1}-\dfrac{x\left(x+1\right)}{\sqrt{x^2+1}}}{x^2+1}=\dfrac{1-x}{\left(x^2+1\right)\sqrt{x^2+1}}\)
5. \(y'=\dfrac{\left(\sqrt{4-3x^2}\right)'}{3x^2-4}=\dfrac{-3x}{\left(3x^2-4\right)\sqrt{4-3x^2}}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a.Hệ thứ nhất kì quặc thật:
\(\Leftrightarrow\sqrt{y^2+xy}+\sqrt{x+y}=\sqrt{x^2+y^2}+2\)
\(\Leftrightarrow\sqrt{x^2+y^2}-\sqrt{y^2+xy}=\sqrt{x+y}-2\)
\(\Leftrightarrow\dfrac{x\left(x-y\right)}{\sqrt{x^2+y^2}+\sqrt{y^2+xy}}=\dfrac{x+y-4}{\sqrt{x+y}+2}\)
\(\Rightarrow\left(x-y\right)\left(x+y-4\right)=\left(\dfrac{\sqrt{x^2+y^2}+\sqrt{y^2+xy}}{x\sqrt{x+y}+2x}\right)\left(x+y-4\right)^2\ge0\) (1)
\(2.\dfrac{x}{2}\sqrt{y-1}+2.\dfrac{y}{2}\sqrt{x-1}\le\dfrac{x^2}{4}+y-1+\dfrac{y^2}{4}+x-1\)
\(\Rightarrow\dfrac{x^2+4y-4}{2}\le\dfrac{x^2+y^2+4x+4y-8}{4}\)
\(\Leftrightarrow x^2-y^2+4y-4x\le0\)
\(\Leftrightarrow\left(x-y\right)\left(x+y-4\right)\le0\) (2)
(1);(2) \(\Rightarrow\left(x-y\right)\left(x+y-4\right)=0\)
Đẳng thức xảy ra khi và chỉ khi \(x=y=2\)
b.
\(x^3-x^2y+2y^2-2xy=0\)
\(\Leftrightarrow x^2\left(x-y\right)-2y\left(x-y\right)=0\)
\(\Leftrightarrow\left(x^2-2y\right)\left(x-y\right)=0\)
\(\Leftrightarrow y=x\) (loại \(x^2-2y=0\) do ĐKXĐ \(x^2-2y-1\ge0\))
Thế vào pt dưới
\(2\sqrt{x^2-2x-1}+\sqrt[3]{x^3-14}=x-2\)
\(\Leftrightarrow2\sqrt{x^2-2x-1}+\dfrac{x^3-14-\left(x-2\right)^3}{\sqrt[3]{\left(x^3-14\right)^2}+\left(x-2\right)\sqrt[3]{x^3-14}+\left(x-2\right)^2}=0\)
\(\Leftrightarrow\sqrt[]{x^2-2x-1}\left(2+\dfrac{6\sqrt[]{x^2-2x-1}}{\sqrt[3]{\left(x^3-14\right)^2}+\left(x-2\right)\sqrt[3]{x^3-14}+\left(x-2\right)^2}\right)=0\)
\(\Leftrightarrow\sqrt{x^2-2x-1}=0\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(=\frac{x-2\sqrt{x}+y+2\sqrt{y}-2\sqrt{xy}+1}{x-2\sqrt{xy}+y-1}\)\(=\frac{\left(\sqrt{x}-\sqrt{y}\right)^2-2\left(\sqrt{x}-\sqrt{y}\right)+1}{\left(\sqrt{x}-\sqrt{y}\right)^2-1}\)
\(=\frac{\left(\sqrt{x}-\sqrt{y}-1\right)^2}{\left(\sqrt{x}-\sqrt{y}+1\right)\left(\sqrt{x}-\sqrt{y}-1\right)}=\frac{\sqrt{x}-\sqrt{y}-1}{\sqrt{x}-\sqrt{y}+1}\)
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Công thức tổng quát:
Áp dụng vào bài toán thì ta có Q=0.75