\(\left\{{}\begin{matrix}x^2+xy+y^2=19\left(x-y\right)^2\\x^2-xy+y^2=7\left(x-y\right)\end{matrix}\right.\)
giải hpt
giải hpt:
1,\(\left\{{}\begin{matrix}x^2y^2-2x+y^2=0\\2x^2-4x+3+y^3=0\end{matrix}\right.\)
2. \(\left\{{}\begin{matrix}\left(x^2-xy\right)\left(xy-y^2\right)=25\\\sqrt{x^2-xy}+\sqrt{xy-y^2}=3\left(x-y\right)\end{matrix}\right.\)
Giải hệ phương trình
\(\left\{{}\begin{matrix}x^2+y^2+xy=13\\x^4+y^4+x^2y^2=91\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}\left(x+y\right)^2-xy=13\\\left(x^2+y^2\right)^2-\left(xy\right)^2=91\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}\left(x+y\right)^2=13+xy\\\left[\left(x+y\right)^2-2xy\right]^2-\left(xy\right)^2=91\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}\left(x+y\right)^2-xy=13\\\left(13-xy\right)^2-\left(xy\right)^2=91\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}xy=3\\\left(x+y\right)^2=16\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x+y=4\\xy=3\end{matrix}\right.\) hoặc x+y = -4
\(\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x+y=4\\xy=3\end{matrix}\right.\\\left\{{}\begin{matrix}x+y=-4\\xy=3\end{matrix}\right.\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x=3\\y=1\end{matrix}\right.\\\left\{{}\begin{matrix}x=-3\\y=-1\end{matrix}\right.\end{matrix}\right.\)hoặc \(\left\{{}\begin{matrix}x=3\\y=1\end{matrix}\right.\)hoặc \(\left\{{}\begin{matrix}x=-1\\y=-3\end{matrix}\right.\)
Mọi người có thể giải thích từ dấu tương đương thứ 3 xuống 4. tại sao lại như vậy k?
giải hpt: \(\left\{{}\begin{matrix}\sqrt{xy+\left(x-y\right)\left(\sqrt{xy}-2\right)}+\sqrt{x}=y+\sqrt{y}\\\left(x+1\right)\left(y+\sqrt{xy}+x-x^2\right)=4\end{matrix}\right.\)
giải hpt: a,\(\left\{{}\begin{matrix}x^2+y^2+xy=7\\x^4+y^4+x^2y^2=21\end{matrix}\right.\) b,\(\left\{{}\begin{matrix}x+y+\dfrac{1}{x}+\dfrac{1}{y}=7\\x^2-y^2+\dfrac{1}{x^2}-\dfrac{1}{y^2}=21\end{matrix}\right.\)
a.
\(\Leftrightarrow\left\{{}\begin{matrix}x^2+y^2+xy=7\\\left(x^2+y^2\right)^2-x^2y^2=21\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x^2+y^2+xy=7\\\left(x^2+y^2+xy\right)\left(x^2+y^2-xy\right)=21\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x^2+y^2+xy=7\\x^2+y^2-xy=3\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x^2+y^2=5\\xy=2\end{matrix}\right.\)
\(\Rightarrow x^2+\left(\dfrac{2}{x}\right)^2=5\)
\(\Leftrightarrow x^4-5x^2=4=0\)
\(\Leftrightarrow...\)
b.
ĐKXĐ: ...
\(\Leftrightarrow\left\{{}\begin{matrix}x+\dfrac{1}{x}+y+\dfrac{1}{y}=7\\\left(x+\dfrac{1}{x}\right)^2-\left(y+\dfrac{1}{y}\right)^2=21\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x+\dfrac{1}{x}+y+\dfrac{1}{y}=7\\\left(x+\dfrac{1}{x}+y+\dfrac{1}{y}\right)\left(x+\dfrac{1}{x}-y-\dfrac{1}{y}\right)=21\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x+\dfrac{1}{x}+y+\dfrac{1}{y}=7\\x+\dfrac{1}{x}-y-\dfrac{1}{y}=3\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x+\dfrac{1}{x}=5\\y+\dfrac{1}{y}=2\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x^2-5x+1=0\\y^2-2y+1=0\end{matrix}\right.\)
\(\Leftrightarrow...\)
giải hệ pt :
a,\(\left\{{}\begin{matrix}x^2+xy+y^2=3\\x+xy+y=-1\end{matrix}\right.\)
\(\left\{{}\begin{matrix}x^3-y^3=7\left(x-y\right)\\x^2+y^2=x+y+2\end{matrix}\right.\)
a, Cộng vế theo vế hai phương trình ta được:
\(x^2+y^2+2xy+x+y=2\)
\(\Leftrightarrow\left(x+y\right)^2+x+y-2=0\)
\(\Leftrightarrow\left(x+y-1\right)\left(x+y+2\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x+y=1\\x+y=-2\end{matrix}\right.\)
TH1: \(x+y=1\)
\(pt\left(2\right)\Leftrightarrow xy+1=-1\Leftrightarrow xy=-2\)
Ta có hệ: \(\left\{{}\begin{matrix}x+y=1\\xy=-2\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x+y=1\\xy=-2\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x=-1\\y=2\end{matrix}\right.\\\left\{{}\begin{matrix}x=2\\y=-1\end{matrix}\right.\end{matrix}\right.\)
TH2: \(x+y=-2\)
\(pt\left(2\right)\Leftrightarrow xy-2=-1\Leftrightarrow xy=1\)
Ta có hệ: \(\left\{{}\begin{matrix}x+y=-2\\xy=1\end{matrix}\right.\Leftrightarrow x=y=-1\)
b, \(\left\{{}\begin{matrix}x^3-y^3=7\left(x-y\right)\\x^2+y^2=x+y+2\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}\left(x-y\right)\left(x^2+y^2+xy-7\right)=0\\x^2+y^2=x+y+2\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}\left[{}\begin{matrix}x=y\\x^2+y^2+xy=7\end{matrix}\right.\\x^2+y^2=x+y+2\end{matrix}\right.\)
TH1: \(\left\{{}\begin{matrix}x=y\\x^2+y^2=x+y+2\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x=y\\x^2-x-1=0\end{matrix}\right.\)
\(\Leftrightarrow x=y=\dfrac{1\pm\sqrt{5}}{2}\)
TH2: \(\left\{{}\begin{matrix}x^2+y^2+xy=7\\x^2+y^2=x+y+2\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}\left(x+y\right)^2-xy=7\\\left(x+y\right)^2-2xy-x-y=2\end{matrix}\right.\)
Đặt \(x+y=u;xy=v\)
Hệ trở thành: \(\left\{{}\begin{matrix}u^2-v=7\\u^2-2v-u=2\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}v=u^2-7\\u^2-2\left(u^2-7\right)-u=2\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}v=u^2-7\\u^2+u-12=0\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}v=u^2-7\\\left[{}\begin{matrix}u=3\\u=-4\end{matrix}\right.\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}v=2\\u=3\end{matrix}\right.\\\left\{{}\begin{matrix}v=9\\u=-4\end{matrix}\right.\end{matrix}\right.\)
Với \(\left\{{}\begin{matrix}v=2\\u=3\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}xy=2\\x+y=3\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x=2\\y=1\end{matrix}\right.\\\left\{{}\begin{matrix}x=1\\y=2\end{matrix}\right.\end{matrix}\right.\)
Với \(\left\{{}\begin{matrix}v=9\\u=-4\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}xy=9\\x+y=-4\end{matrix}\right.\left(vn\right)\)
giải hpt:
1, \(\left\{{}\begin{matrix}x^2y^2+4=2y^2\\\left(xy+2\right)\left(y-x\right)=x^3y^3\end{matrix}\right.\)
2, \(\left\{{}\begin{matrix}x^2+y^2-4xy\left(\dfrac{2}{x-y}-1\right)=4\left(4+xy\right)\\\sqrt{x-y}+3\sqrt{2y^2-y+1}=2y^2-x+3\end{matrix}\right.\)
giải HPT
a) \(\left\{{}\begin{matrix}\left(x+3\right)\left(y-5\right)=xy\\\left(2x-y\right)\left(y+15\right)=2xy\end{matrix}\right.\)
b) \(\left\{{}\begin{matrix}\sqrt{4x}-3y+4z^2=-2\\\sqrt{3x}+2y-3z^2=1\\-3\sqrt{x}+y+2z^2=4\end{matrix}\right.\)
\(\left\{{}\begin{matrix}x^3y\left(1+y\right)+x^2y^2\left(2+y\right)+xy^3=30\\x^2y+x\left(1+y+y^2\right)+y=11\end{matrix}\right.\)
Ta có hpt \(\left\{{}\begin{matrix}xy+3y-5x-15=xy\\2xy+30x-y^2-15y=0\end{matrix}\right.\)\(\Leftrightarrow\left\{{}\begin{matrix}5x=3y-15\\6\left(3y-15\right)-y^2-15y=0\end{matrix}\right.\)
Ta có pt (2) \(\Leftrightarrow3y-y^2-80=0\Leftrightarrow y^2-3y+80=0\left(VN\right)\)
=> hpy vô nghiệm
c) Ta có hpt \(\Leftrightarrow\left\{{}\begin{matrix}xy\left(x+y\right)\left(xy+x+y\right)=30\\xy\left(x+y\right)+xy+x+y=11\end{matrix}\right.\)
Đặt j\(xy\left(x+y\right)=a;xy+x+y=b\), ta có hpt
\(\left\{{}\begin{matrix}ab=30\\a+b=11\end{matrix}\right.\)\(\Leftrightarrow\left[{}\begin{matrix}a=5;b=6\\a=6;b=5\end{matrix}\right.\)
với a=5;b=6, ta có \(\left\{{}\begin{matrix}xy\left(x+y\right)=5\\xy+x+y=6\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}xy=1;x+y=5\\xy=5;x+y=1\end{matrix}\right.\)
đến đây thì thế y hoặc x ra pt bậc 2, còn TH còn lại bn tự giải nhé !
b) Ta có hpt <=> \(\left\{{}\begin{matrix}2\sqrt{x}-3y+2=-4z^2\\2\sqrt{3x}+4y-2=6z^2\\-3\sqrt{x}+y-4=-2z^2\end{matrix}\right.\)
cộng 3 vế của 3 pt, ta có \(\left(2\sqrt{3}-1\right)\sqrt{x}=4\Leftrightarrow\sqrt{x}=\dfrac{4}{2\sqrt{3}-1}\Leftrightarrow x=\dfrac{16}{\left(2\sqrt{3}-1\right)^2}\)
đến đây thay căn(x)=...vào và đặt z^2=m, ta sẽ ra 1 hệ mới chỉ có 2 ẩn y và m bậc 1 , lát thế vào sẽ ra bậc 2 thì dễ rồi !
giải hpt \(\left\{{}\begin{matrix}\dfrac{1-xy}{x\left(1+y^2\right)}=\dfrac{2}{5}\\\dfrac{1-xy}{y\left(1+x^2\right)}=\dfrac{1}{2}\end{matrix}\right.\)
giải hpt: \(\left\{{}\begin{matrix}x^2+4x+y=18\\xy\left(x+1\right)\left(y+1\right)=72\end{matrix}\right.\)
Mình cảm thấy đề cứ sai sai. Bạn xem lại xem chứ nghiệm rất xấu.