giải hệ phương trình \(\left\{{}\begin{matrix}\dfrac{1}{x^2}+\dfrac{1}{y^2}=1\\\sqrt{x^2-1}+\sqrt{y^2-1}=\sqrt{xy}+2\end{matrix}\right.\)
giải hệ phương trình
\(\left\{{}\begin{matrix}2x^2-xy=1\\\dfrac{1}{\sqrt{x}}-y-\dfrac{1}{\sqrt{y}}=x\end{matrix}\right.\)
Lời giải:
ĐK: $x,y>0$
PT$(2)\Rightarrow \frac{1}{\sqrt{x}}-x=y+\frac{1}{\sqrt{y}}>0$
$\Rightarrow 1-x\sqrt{x}>1\Rightarrow 1>x$
Quay lại PT $(1)$:
$2x^2=xy+1$
Nếu $y\geq x$ thì: $2x^2=xy+1\geq x^2+1\Leftrightarrow x^2\geq 1\Rightarrow x\geq 1$ (vô lý vì $x<1$)
$\Rightarrow 0<y<x$
Khi đóTại PT$(2)$: $x+y=\frac{1}{\sqrt{x}}-\frac{1}{\sqrt{y}}<0$ (vô lý vì $x,y>0$)
Vậy HPT vô nghiệm
Giải hệ phương trình: \(\left\{{}\begin{matrix}\sqrt{xy+\dfrac{x-y}{x^2+y^2+1}}+\sqrt{x}=y+\sqrt{y}\\\left|x-1\right|+\left|y-2\right|=1+x^2-y^2\end{matrix}\right.\)
\(\left\{{}\begin{matrix}\sqrt{xy+\dfrac{x-y}{x^2+y^2+1}}+\sqrt{x}=y+\sqrt{y}\left(1\right)\\\left|x-1\right|+\left|y-2\right|=1+x^2-y^2\left(2\right)\end{matrix}\right.\)
ĐKXĐ: \(\left\{{}\begin{matrix}x\ge0\\y\ge0\\xy+\dfrac{x-y}{x^2+y^2+1}\ge0\end{matrix}\right.\)
\(\left(1\right)\Leftrightarrow\sqrt{xy+\dfrac{x-y}{x^2+y^2+1}}-y=\sqrt{y}-\sqrt{x}\)
\(\Leftrightarrow\dfrac{y\left(x-y\right)+\dfrac{x-y}{x^2+y^2+1}}{\sqrt{xy+\dfrac{x-y}{x^2+y^2+1}}+y}=\dfrac{x-y}{-xy}\Leftrightarrow\left(x-y\right)\left[\dfrac{y+\dfrac{1}{x^2+y^2+1}}{\sqrt{xy+\dfrac{x-y}{x^2+y^2+1}}+y}+xy\right]=0\Leftrightarrow x=y\).
Thay x = y vào (2) ta có \(\left|y-1\right|+\left|y-2\right|=1\). (*)
Ta có \(\left|y-1\right|+\left|y-2\right|=\left|y-1\right|+\left|2-y\right|\ge y-1+2-y=1\).
Mà đẳng thức xảy ra ở (1) nên ta phải có \(1\le y\le2\). (TMĐK)
Vậy pt đã cho có vô số nghiệm \(x=y=k\) với \(1\le k\le2\)
giải hệ phương trình
\(\left\{{}\begin{matrix}\sqrt{x-2}+\sqrt{y-3}=3\\2\sqrt{x-2}-3\sqrt{y-3}=-4\end{matrix}\right.\)
\(\left\{{}\begin{matrix}\dfrac{3x}{x+1}+\dfrac{2}{y+4}=4\\\dfrac{2x}{x+1}-\dfrac{5}{y+4}=4\end{matrix}\right.\)
a.
ĐKXĐ: \(\left\{{}\begin{matrix}x\ge2\\y\ge3\end{matrix}\right.\)
\(\left\{{}\begin{matrix}3\sqrt{x-2}+3\sqrt{y-3}=9\\2\sqrt{x-2}-3\sqrt{y-3}=-4\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}3\sqrt{x-2}+3\sqrt{y-3}=9\\5\sqrt{x-2}=5\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}3\sqrt{x-2}+3\sqrt{y-3}=9\\\sqrt{x-2}=1\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}\sqrt{x-2}=1\\\sqrt{y-3}=2\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}x=3\\y=7\end{matrix}\right.\)
b.
ĐKXĐ: \(\left\{{}\begin{matrix}x\ne-1\\y\ne-4\end{matrix}\right.\)
\(\left\{{}\begin{matrix}\dfrac{15x}{x+1}+\dfrac{10}{y+4}=20\\\dfrac{4x}{x+1}-\dfrac{10}{y+4}=8\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}\dfrac{15x}{x+1}+\dfrac{10}{y+4}=20\\\dfrac{19x}{x+1}=28\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}\dfrac{x}{x+1}=\dfrac{28}{19}\\\dfrac{1}{y+4}=-\dfrac{4}{19}\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}19x=28x+28\\4y+16=-19\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x=-\dfrac{28}{9}\\y=-\dfrac{35}{4}\end{matrix}\right.\)
Giải hệ bằng phương pháp phân tích nhân tử
a) \(\left\{{}\begin{matrix}\dfrac{1}{x^2}+\dfrac{1}{y^2}=1\\\sqrt{x^2-1}+\sqrt{y^2-1}=\sqrt{xy+2}\end{matrix}\right.\)
b) \(\left\{{}\begin{matrix}\left(x-y\right)\left(x^2+y^2\right)=13\\\left(x+y\right)\left(x^2-y^2\right)=25\end{matrix}\right.\)
Giải hệ phương trình: \(\left\{{}\begin{matrix}\dfrac{1}{x}-\sqrt{y-1}=4\\\dfrac{2}{x}-\sqrt{y-1}=2\end{matrix}\right.\)
Đặt 1/x=a; căn(y-1)=b
\(\Leftrightarrow\left\{{}\begin{matrix}a-b=4\\2a-b=2\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}a=-2\\b=a+4=2\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=-\dfrac{1}{2}\\y=5\end{matrix}\right.\)
Đặt: \(\left[{}\begin{matrix}a=\dfrac{1}{x}\\b=\sqrt{y-1}\end{matrix}\right.\)
\(=>\left\{{}\begin{matrix}a-b=4\\2a-b=2\end{matrix}\right.\)\(\Leftrightarrow\left\{{}\begin{matrix}2a-2b=8\\2a-b=2\end{matrix}\right.\)\(\Leftrightarrow\left\{{}\begin{matrix}-b=6\\a-b=4\end{matrix}\right.\)\(\Leftrightarrow\left\{{}\begin{matrix}b=-6\\a+6=4\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}b=-6\\a=-2\end{matrix}\right.\) Thay: \(\left\{{}\begin{matrix}\dfrac{1}{x}=-2\\\sqrt{y-1}=-6\end{matrix}\right.\)\(\Leftrightarrow\left\{{}\begin{matrix}x=-\dfrac{1}{2}\\y=37\end{matrix}\right.\)
Giải hệ phương trình
\(\left\{{}\begin{matrix}\sqrt{x+1}+\dfrac{2y}{y+1}=2\\2\sqrt{x+1}-\dfrac{1}{y+1}=\dfrac{3}{2}\end{matrix}\right.\)
Có : \(\left\{{}\begin{matrix}\sqrt{x+1}+\dfrac{2y}{y+1}=2\\2\sqrt{x+1}-\dfrac{1}{y+1}=\dfrac{3}{2}\end{matrix}\right.\)
-> \(\left\{{}\begin{matrix}2\sqrt{x+1}+\dfrac{4y}{y+1}=4\\2\sqrt{x+1}-\dfrac{1}{y+1}=\dfrac{3}{2}\end{matrix}\right.\)
-> \(\left\{{}\begin{matrix}2\sqrt{x+1}+\dfrac{4y}{y+1}-2\sqrt{x+1}+\dfrac{1}{y+1}=4-\dfrac{3}{2}\\2\sqrt{x+1}-\dfrac{1}{y+1}=\dfrac{3}{2}\end{matrix}\right.\)
-> \(\left\{{}\begin{matrix}\dfrac{4y+1}{y+1}=\dfrac{5}{2}\\\sqrt{x+1}=\dfrac{\dfrac{3}{2}+\dfrac{1}{y+1}}{2}\end{matrix}\right.\)
-> \(\left\{{}\begin{matrix}2.\left(4y+1\right)=5.\left(y+1\right)\\\sqrt{x+1}=\dfrac{\dfrac{3}{2}+\dfrac{1}{y+1}}{2}\end{matrix}\right.\)
-> \(\left\{{}\begin{matrix}8y+2=5y+5\\\sqrt{x+1}=\dfrac{\dfrac{3}{2}+\dfrac{1}{y+1}}{2}\end{matrix}\right.\)
-> \(\left\{{}\begin{matrix}3y=3->y=1\\\sqrt{x+1}=\dfrac{\dfrac{3}{2}+\dfrac{1}{1+1}}{2}\end{matrix}\right.\)
-> \(\left\{{}\begin{matrix}y=1\\\sqrt{x+1}=1\end{matrix}\right.\)
-> \(\left\{{}\begin{matrix}y=1\\x=0\end{matrix}\right.\)
Vậy .........
Giải các hệ phương trình sau bằng phương pháp cộng đại số:
a) \(\left\{{}\begin{matrix}\sqrt{2}x-y=3\\x+\sqrt{2}y=\sqrt{2}\end{matrix}\right.\)
b) \(\left\{{}\begin{matrix}\dfrac{x}{2}-2y=\dfrac{3}{4}\\2x+\dfrac{y}{3}=-\dfrac{1}{3}\end{matrix}\right.\)
c) \(\left\{{}\begin{matrix}\dfrac{2x-3y}{4}-\dfrac{x+y-1}{5}=2x-y-1\\\dfrac{x+y-1}{3}+\dfrac{4x-y-2}{4}=\dfrac{2x-y-3}{6}\end{matrix}\right.\)
a) Ta có: \(\left\{{}\begin{matrix}\sqrt{2}x-y=3\\x+\sqrt{2}y=\sqrt{2}\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}\sqrt{2}x-y=3\\\sqrt{2}x+2y=2\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}-3y=1\\x+\sqrt{2}y=\sqrt{2}\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=-\dfrac{1}{3}\\x=\sqrt{2}-\sqrt{2}y\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}y=-\dfrac{1}{3}\\x=\sqrt{2}-\sqrt{2}\cdot\dfrac{-1}{3}=\dfrac{4\sqrt{2}}{3}\end{matrix}\right.\)
Vậy: Hệ phương trình có nghiệm duy nhất là \(\left\{{}\begin{matrix}x=\dfrac{4\sqrt{2}}{3}\\y=-\dfrac{1}{3}\end{matrix}\right.\)
b) Ta có: \(\left\{{}\begin{matrix}\dfrac{x}{2}-2y=\dfrac{3}{4}\\2x+\dfrac{y}{3}=-\dfrac{1}{3}\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}2x-8y=3\\2x+\dfrac{1}{3}y=-\dfrac{1}{3}\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}-\dfrac{25}{3}y=\dfrac{10}{3}\\2x-8y=3\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}y=-\dfrac{2}{5}\\2x=3+8y=3+8\cdot\dfrac{-2}{5}=-\dfrac{1}{5}\end{matrix}\right.\)
hay \(\left\{{}\begin{matrix}x=-\dfrac{1}{10}\\y=-\dfrac{2}{5}\end{matrix}\right.\)
Vậy: Hệ phương trình có nghiệm duy nhất là \(\left\{{}\begin{matrix}x=-\dfrac{1}{10}\\y=-\dfrac{2}{5}\end{matrix}\right.\)
c) Ta có: \(\left\{{}\begin{matrix}\dfrac{2x-3y}{4}-\dfrac{x+y-1}{5}=2x-y-1\\\dfrac{x+y-1}{3}+\dfrac{4x-y-2}{4}=\dfrac{2x-y-3}{6}\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}\dfrac{5\left(2x-3y\right)}{20}-\dfrac{4\left(x+y-1\right)}{20}=\dfrac{20\left(2x-y-1\right)}{20}\\\dfrac{4\left(x+y-1\right)}{12}+\dfrac{3\left(4x-y-2\right)}{12}=\dfrac{2\left(2x-y-3\right)}{12}\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}10x-15y-4x-4y+4=40x-20y-20\\4x+4y-4+12x-3y-6=4x-2y-6\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}6x-19y+4-40x+20y+20=0\\16x+y-10-4x+2y+6=0\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}-34x+y=-24\\12x+3y=4\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}-102x+3y=-72\\12x+3y=4\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}-114x=-76\\12x+3y=4\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{2}{3}\\12\cdot\dfrac{2}{3}+3y=4\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{2}{3}\\3y=4-8=-4\end{matrix}\right.\)
hay \(\left\{{}\begin{matrix}x=\dfrac{2}{3}\\y=-\dfrac{4}{3}\end{matrix}\right.\)
Vậy: Hệ phương trình có nghiệm duy nhất là \(\left\{{}\begin{matrix}x=\dfrac{2}{3}\\y=-\dfrac{4}{3}\end{matrix}\right.\)
Giải hệ phương trình:
a)\(\left\{{}\begin{matrix}\dfrac{1}{x}+\dfrac{1}{y}+\dfrac{1}{z}=2\\\dfrac{2}{xy}-\dfrac{1}{z^2}=4\end{matrix}\right.\)
b)\(\left\{{}\begin{matrix}y=2\sqrt{x-1}\\\sqrt{x+y}=x^2-y\end{matrix}\right.\)
c)\(\left\{{}\begin{matrix}xy-\dfrac{x}{y}=9.6\\xy-\dfrac{y}{x}=7.5\end{matrix}\right.\)
d)\(\left\{{}\begin{matrix}\dfrac{1}{x}+\dfrac{1}{y}+\dfrac{1}{z}=2\\\dfrac{2}{xy}-\dfrac{1}{z^2}=4\end{matrix}\right.\)
Giải hệ phương trình: \(\left\{{}\begin{matrix}\dfrac{3}{\sqrt[]{x+y}}-\dfrac{2}{\sqrt[]{x-y}}=4\\\dfrac{2}{\sqrt[]{x+y}}+\dfrac{1}{\sqrt[]{x-y}}=5\end{matrix}\right.\)
Ta có: \(\left\{{}\begin{matrix}\dfrac{3}{\sqrt{x+y}}-\dfrac{2}{\sqrt{x-y}}=4\\\dfrac{2}{\sqrt{x+y}}-\dfrac{1}{\sqrt{x-y}}=5\end{matrix}\right.\)
Đặt: \(t=\sqrt{x+y}\) và \(k=\sqrt{x-y}\)
\(\Leftrightarrow\left\{{}\begin{matrix}\dfrac{3}{t}-\dfrac{2}{k}=4\\\dfrac{2}{t}+\dfrac{1}{k}=5\end{matrix}\right.\)
Ta lại đặt: \(a=\dfrac{1}{t}\) và \(u=\dfrac{1}{k}\)
\(\Leftrightarrow\left\{{}\begin{matrix}3a-2u=4\\2a+u=5\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}3a-2u=4\\4a+2u=10\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}3a-2u=4\\7a=14\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}6-2u=4\\a=2\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}u=1\\a=2\end{matrix}\right.\)
Mà:
\(u=1\Rightarrow\dfrac{1}{k}=1\Rightarrow k=1\)
\(a=2\Rightarrow\dfrac{1}{t}=2\Rightarrow t=\dfrac{1}{2}\)
Ta lại có:
\(k=1\Rightarrow\sqrt{x+y}=1\)
\(t=\dfrac{1}{2}\Rightarrow\sqrt{x-y}=\dfrac{1}{2}\)
Ta có hệ:
\(\left\{{}\begin{matrix}\sqrt{x-y}=1\\\sqrt{x+y}=\dfrac{1}{2}\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x-y=1\\x+y=\dfrac{1}{4}\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x-y=1\\2x=\dfrac{5}{4}\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}\dfrac{5}{8}-y=1\\x=\dfrac{5}{8}\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}y=-\dfrac{3}{8}\\x=\dfrac{5}{8}\end{matrix}\right.\)
Vậy \(x-\dfrac{5}{8};y=-\dfrac{3}{8}\)
Đặt 1/căn x+y=a; 1/căn x-y=b
Theo đề, ta có hệ:
3a-2b=4 và 2a+b=5
=>a=2 và b=1
=>x+y=1/4 và x-y=1
=>x=5/8 và y=-3/8
Giải hệ phương trình:
1. \(\left\{{}\begin{matrix}x+3=2\sqrt{\left(3y-x\right)\left(y+1\right)}\\\sqrt{3y-2}-\sqrt{\dfrac{x+5}{2}}=xy-2y-2\end{matrix}\right.\)
2. \(\left\{{}\begin{matrix}\sqrt{2y^2-7y+10-x\left(y+3\right)}+\sqrt{y+1}=x+1\\\sqrt{y+1}+\dfrac{3}{x+1}=x+2y\end{matrix}\right.\)
3. \(\left\{{}\begin{matrix}\sqrt{4x-y}-\sqrt{3y-4x}=1\\2\sqrt{3y-4x}+y\left(5x-y\right)=x\left(4x+y\right)-1\end{matrix}\right.\)
4. \(\left\{{}\begin{matrix}9\sqrt{\dfrac{41}{2}\left(x^2+\dfrac{1}{2x+y}\right)}=3+40x\\x^2+5xy+6y=4y^2+9x+9\end{matrix}\right.\)
5. \(\left\{{}\begin{matrix}\sqrt{xy+\left(x-y\right)\left(\sqrt{xy}-2\right)}+\sqrt{x}=y+\sqrt{y}\\\left(x+1\right)\left[y+\sqrt{xy}+x\left(1-x\right)\right]=4\end{matrix}\right.\)
6. \(\left\{{}\begin{matrix}x^4-x^3+3x^2-4y-1=0\\\sqrt{\dfrac{x^2+4y^2}{2}}+\sqrt{\dfrac{x^2+2xy+4y^2}{3}}=x+2y\end{matrix}\right.\)
7. \(\left\{{}\begin{matrix}x^3-12z^2+48z-64=0\\y^3-12x^2+48x-64=0\\z^3-12y^2+48y-64=0\end{matrix}\right.\)