giai phuong trinh xy+xz=2(x+y+z); xy+yz=3(x+y+z); xz+yz=4(x+y+z)
Giai he phuong trinh:
a) \(\left\{{}\begin{matrix}\left(x+y\right).\left(y+z\right)=187\\\left(y+z\right).\left(z+x\right)=154\\\left(z+x\right).\left(x+y\right)=238\end{matrix}\right.\)
b) \(\left\{{}\begin{matrix}x^2+y^2+z^2=xy+yz+xz\\x^{2019}+y^{2019}+z^{2019}=3^{2020}\end{matrix}\right.\)
giai he phuong trinh
x+y+xy=11y+z+zy=47z+x+zx=35\(x+y+xy=11\Leftrightarrow x\left(y+1\right)+y+1=12\Leftrightarrow\left(x+1\right)\left(y+1\right)=12\)(1)
\(y\left(z+1\right)+z+1=48\Leftrightarrow\left(y+1\right)\left(z+1\right)=48\left(2\right)\)
\(z\left(x+1\right)+x+1=36\Leftrightarrow\left(z+1\right)\left(x+1\right)=36\left(3\right)\)
Lấy vế nhân vế của (1) (2) và (3) ta đc : \(\left[\left(x+1\right)\left(y+1\right)\left(z+1\right)\right]^2=12\cdot36\cdot48=144^2\)
=> \(\left(x+1\right)\left(y+1\right)\left(z+1\right)=144\) hoặc = -144
(+) Với \(\left(x+1\right)\left(y+1\right)\left(z+1\right)=144\)
=> z + 1 = 144 : 12 = 12 => z = 11
=> \(x+1=144:48=3\Rightarrow x=2\)
=> \(y+1=144:36=4\Leftrightarrow y=3\)
(+) Với ( x +1 )( y +1 )( z + 1 ) = -144 ( tương tự )
giai phuong trinh x^2+y^2+z^2=y(x+z)
\(PT\Leftrightarrow x^2+y^2+z^2=xy+yz\)
\(\Leftrightarrow4x^2+4y^2+4z^2=4xy+4yz\)
\(\Leftrightarrow4x^2+4y^2+4z^2-4xy-4yz=0\)
\(\Leftrightarrow\left(4x^2-4xy+y^2\right)+\left(4z^2-4yz+y^2\right)+2y^2=0\)
\(\Leftrightarrow\left(2x-y\right)^2+\left(2z-y\right)^2+2y^2=0\)
Vì \(\left(2x-y\right)^2+\left(2z-y\right)^2+2y^2\ge0\forall x;y;z\)
Dấu "=" xảy ra khi \(x=y=z=0\)
giai phuong trinh x2-xy+y2=3
\(x^2-xy+y^2=3\)
\(\Leftrightarrow\)\(x^2-xy+y^2-3=0\)
Để phương trình có nghiệm thì:
\(\Delta=y^2-4\left(y^2-3\right)\ge0\)
\(\Leftrightarrow\)\(y^2-4y^2+12\ge0\)
\(\Leftrightarrow\)\(-3y^2\ge-12\)
\(\Leftrightarrow\)\(y^2\le4\)
\(\Rightarrow\)\(y=\left\{0;\pm1;\pm2\right\}\)
đến đây tự lm tiếp nhé, thay y vào pt ban đầu rồi giải tìm x là xog
giai he phuong trinh\(\left\{{}\begin{matrix}x^2+y^2-xy=19\\x+y+xy=-7\end{matrix}\right.\)
giai he phuong trinh
x+2\x+1\y=4
1\x^2+1\xy+x\y=3
Giai phuong trinh x2+ y22+z22=y(x+z)
Giai phuong trinh nghiem nguyên
x^2-xy+y^2=3
giai he phuong trinh sau :
x^3 - x^2 y^2 - y^3 + 1 = 0 va x^3 + xy - 2 = 0