Question

[Huyền Trang]

Mọi người giải giúp em với ạ :)) Help me !!

Answer 1

[An Thy]

\(\left\{{}\begin{matrix}2\left(x+y\right)+\sqrt{x+1}=4\\\left(x+y\right)-3\sqrt{x+1}=-5\end{matrix}\right.\left(x\ge-1\right)\)

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

\(\Rightarrow\left\{{}\begin{matrix}2a+b=4\\a-3b=-5\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}2a+b=4\left(1\right)\\2a-6b=-10\left(2\right)\end{matrix}\right.\)

Lấy \(\left(1\right)-\left(2\right)\Rightarrow7b=14\Rightarrow b=2\Rightarrow2a=4-2=2\Rightarrow a=1\)

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