a.

ĐKXĐ: \(1\le x\le7\)

\(\Leftrightarrow x-1-2\sqrt{x-1}+2\sqrt{7-x}-\sqrt{\left(x-1\right)\left(7-x\right)}=0\)

\(\Leftrightarrow\sqrt{x-1}\left(\sqrt{x-1}-2\right)-\sqrt{7-x}\left(\sqrt{x-1}-2\right)=0\)

\(\Leftrightarrow\left(\sqrt{x-1}-\sqrt{7-x}\right)\left(\sqrt{x-1}-2\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}\sqrt{x-1}=\sqrt{7-x}\\\sqrt{x-1}=2\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x-1=7-x\\x-1=4\end{matrix}\right.\)

\(\Leftrightarrow...\)

b. ĐKXĐ: ...

Biến đổi pt đầu:

\(x\left(y-1\right)-\left(y-1\right)^2=\sqrt{y-1}-\sqrt{x}\)

Đặt \(\left\{{}\begin{matrix}\sqrt{x}=a\ge0\\\sqrt{y-1}=b\ge0\end{matrix}\right.\)

\(\Rightarrow a^2b^2-b^4=b-a\)

\(\Leftrightarrow b^2\left(a+b\right)\left(a-b\right)+a-b=0\)

\(\Leftrightarrow\left(a-b\right)\left(b^2\left(a+b\right)+1\right)=0\)

\(\Leftrightarrow a=b\)

\(\Leftrightarrow\sqrt{x}=\sqrt{y-1}\Rightarrow y=x+1\)

Thế vào pt dưới:

\(3\sqrt{5-x}+3\sqrt{5x-4}=2x+7\)

\(\Leftrightarrow3\left(x-\sqrt{5x-4}\right)+7-x-3\sqrt{5-x}=0\)

\(\Leftrightarrow\dfrac{3\left(x^2-5x+4\right)}{x+\sqrt{5x-4}}+\dfrac{x^2-5x+4}{7-x+3\sqrt{5-x}}=0\)

\(\Leftrightarrow\left(x^2-5x+4\right)\left(\dfrac{3}{x+\sqrt{5x-4}}+\dfrac{1}{7-x+3\sqrt{5-x}}\right)=0\)

\(\Leftrightarrow...\)

Giải hệ phương trình: \(\left\{\begin{matrix} xy-y^2-x+2y=\sqrt{y-1}+1-\sqrt{x} - Hy Vũ

ĐK : \(x\ge-2;y\ge-3\)

pt (1) <=> \(x^3+x=\left(y+1\right)^3+\left(y+1\right)\)

<=> \(\left(y+1\right)^3-x^3+\left(y+1\right)-x=0\)

<=> \(\left(y+1-x\right)\left(\left(y+1\right)^2+\left(y+1\right)x+x^2+1\right)=0\)

<=> \(y+1-x=0\) vì \(\left(y+1\right)^2+\left(y+1\right)x+x^2+1>0\)dễ chứng minh.

<=> \(x=y+1\)(1')

pt (2) <=> \(\sqrt{\left(\sqrt{x+2}-2\right)^2}+\sqrt{\left(\sqrt{y+3}-3\right)^2}=1\)

<=> \(\left|\sqrt{x+2}-2\right|+\left|\sqrt{y+3}-3\right|=1\)(2')

Thế (1') vào (2') ta có: \(\left|\sqrt{y+3}-2\right|+\left|\sqrt{y+3}-3\right|=1\)

Có: \(\left|\sqrt{y+3}-2\right|+\left|\sqrt{y+3}-3\right|=\left|\sqrt{y+3}-2\right|+\left|3-\sqrt{y+3}\right|\ge1\)

Do đó: \(\left|\sqrt{y+3}-2\right|+\left|\sqrt{y+3}-3\right|=1\)<=> \(\left(\sqrt{y+3}-2\right)\left(3-\sqrt{y+3}\right)\ge0\)

<=> \(2\le\sqrt{y+3}\le3\)

<=> \(4\le y+3\le9\)

<=> \(1\le y\le6\)(tm) 

Khi đó: x = y + 1 với mọi y thỏa mãn \(1\le y\le6\)

Vậy tập nghiệm  \(S=\left\{\left(y+1;y\right):1\le y\le6\right\}\)

\(\int^{\sqrt{x^3}-\sqrt{y^3}=8\sqrt{x}+2\sqrt{y}\left(1\right)}_{x-3y=6\left(2\right)}\)

ĐK: \(x,y\ge0\)

(2) => x = 6 + 3y  (3)

(1) => \(\sqrt{x^3}-8\sqrt{x}=\sqrt{y^3}+2\sqrt{y}\) 

\(\Rightarrow\sqrt{x}\left(\sqrt{x^2}-8\right)=\sqrt{y}\left(\sqrt{y^2}+2\right)\)

\(\Rightarrow\sqrt{x}\left(x-8\right)=\sqrt{y}\left(y+2\right)\)  (4)

Thay (3) vào (4) ta đc:

\(\sqrt{6+3y}\left(6+3y-8\right)=\sqrt{y}\left(y+2\right)\)

\(\Rightarrow\left(6+3y\right)\left(3y-2\right)^2=y\left(y+2\right)^2\)

\(\Rightarrow\left(6+3y\right)\left(9y^2-12y+4\right)=y\left(y^2+4y+4\right)\)

\(\Rightarrow54y^2-72y+24+27y^3-36y^2+12y=y^3+4y^2+4y\)

\(\Rightarrow26y^3+14y^2-64y+24=0\)

\(\Rightarrow y=-2\)     (loại)

hoặc y = 1            (nhận)

hoặc y = \(\frac{6}{13}\)       (nhận)

+) Với y = 1 => x = 9

+) Với y = \(\frac{6}{13}\) => x = \(\frac{96}{13}\)

Vậy hệ có 2 cặp nghiệm (x;y) = (9;1) hoặc (x;y) = (\(\frac{96}{13};\frac{6}{13}\))

olm dang duyet

thôi thì 2 tiếng nữa way lại

kho qua tui xin chiu

bài này lượm ở đâu v

\(\Leftrightarrow\sqrt{x^3}-\sqrt{y^3}=-\left(\sqrt{y}-\sqrt{x}\right)\left(y+\sqrt{x}\sqrt{y}+x\right)\)

\(\Rightarrow8\sqrt{x+2\sqrt{y}}=8\sqrt{2\sqrt{y}+x}\)

\(\Rightarrow-\sqrt{y^3}-8\sqrt{2\sqrt{y}+x}+\sqrt{x^3}=0\)

\(\Rightarrow\sqrt{y}=\left(\sqrt{x^3}-8\sqrt{2\sqrt{y}+x}\right)^{\frac{1}{3}}\)

=>pt đc xác định dưới dạng hàm ẩn :\(\sqrt{x^3}-\sqrt{y^3}=8\sqrt{2\sqrt{y}+x}\)

1: \(\left\{{}\begin{matrix}x\sqrt{2}-3y=1\\2x+y\sqrt{2}=-2\end{matrix}\right.\)

=>\(\left\{{}\begin{matrix}2x-3\sqrt{2}\cdot y=\sqrt{2}\\2x+y\sqrt{2}=-2\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}-4\sqrt{2}\cdot y=\sqrt{2}+2\\2x+y\sqrt{2}=-2\end{matrix}\right.\)

=>\(\left\{{}\begin{matrix}y=\dfrac{2+\sqrt{2}}{-4\sqrt{2}}=\dfrac{-\sqrt{2}-1}{4}\\2x=-2-y\sqrt{2}=-2+\sqrt{2}\cdot\dfrac{\sqrt{2}+1}{4}=\dfrac{-6+\sqrt{2}}{4}\end{matrix}\right.\)

=>\(\left\{{}\begin{matrix}y=\dfrac{-\sqrt{2}-1}{4}\\x=\dfrac{-6+\sqrt{2}}{8}\end{matrix}\right.\)

2: \(\left\{{}\begin{matrix}5x\sqrt{3}+y=2\sqrt{2}\\x\sqrt{6}-y\sqrt{2}=2\end{matrix}\right.\)

=>\(\left\{{}\begin{matrix}5x\sqrt{6}+y\sqrt{2}=4\\x\sqrt{6}-y\sqrt{2}=2\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}6x\cdot\sqrt{6}=6\\x\sqrt{6}-y\sqrt{2}=2\end{matrix}\right.\)

=>\(\left\{{}\begin{matrix}x=\dfrac{1}{\sqrt{6}}=\dfrac{\sqrt{6}}{6}\\y\sqrt{2}=x\sqrt{6}-2=1-2=-1\end{matrix}\right.\)

=>\(\left\{{}\begin{matrix}x=\dfrac{\sqrt{6}}{6}\\y=-\dfrac{\sqrt{2}}{2}\end{matrix}\right.\)