Question

[Nguyễn Khắc Quang]

Cho ba số x,y,z thỏa mãn: \(x^2+2y+1=0\) , \(y^2+2z+1=0\), \(z^2+2x+1=0\).

Tính giá trị của biểu thức: \(A=x^{2015}+y^{2016}+z^{2017}\)

Answer 1

[Greninja]

Ta có : \(x^2+2y+1=0;y^2+2z+1=0;z^2+2x+1=0\)

\(\Rightarrow x^2+2y+1=y^2+2z+1=z^2+2x+1\)

\(\Rightarrow x^2+2y+1-y^2-2z-1-z^2-2x-1=0\)

\(\Rightarrow\left(x^2-2x+1\right)-\left(y^2-2y+1\right)-\left(z^2+2z+1\right)=0\)

\(\Rightarrow\left(x-1\right)^2-\left(y-1\right)^2-\left(z+1\right)^2=0\)

\(\Leftrightarrow\hept{\begin{cases}\left(x-1\right)^2=0\\\left(y-1\right)^2=0\\\left(z+1\right)^2=0\end{cases}\Leftrightarrow}\hept{\begin{cases}x-1=0\\y-1=0\\z+1=0\end{cases}\Leftrightarrow}\hept{\begin{cases}x=1\\y=1\\z=-1\end{cases}}\)

Thay \(x=1;y=1;z=-1\)vào A ta có :

\(A=1^{2015}+1^{2016}+\left(-1\right)^{2017}=1+1-1=1\)

Vậy A = 1

Answer 2

[Yuri Sweet[𝕿𝖊𝖆𝖒 𝕹𝖊𝖕𝖆𝖑]]

Từ \(\hept{\begin{cases}x^2+2y+1=0\\y^2+2z+1=0\\z^2+2x+1=0\end{cases}}\)

\(\Rightarrow x^2+2y+1+y^2+2z+1+z^2+2x+1=0\)

\(\Rightarrow\left(x^2+2x+1\right)+\left(y^2+2y+1\right)+\left(z^2+2z+1\right)=0\)

\(\Rightarrow\left(x+1\right)^2+\left(y+1\right)^2+\left(z+1\right)^2=0\left(1\right)\)

Vì \(\hept{\begin{cases}\left(x+1\right)^2\ge0\forall x\\\left(y+1\right)^2\ge0\forall y\\\left(z+1\right)^2\ge0\forall z\end{cases}\left(2\right)}\)

Từ \(\left(1\right)\)và \(\left(2\right)\):

\(\Rightarrow\hept{\begin{cases}\left(x+1\right)^2=0\\\left(y+1\right)^2=0\\\left(z+1\right)^2=0\end{cases}}\)

\(\Rightarrow\hept{\begin{cases}x+1=0\\y+1=0\\z+1=0\end{cases}}\)

\(\Rightarrow x=y=z=-1\)

\(\Rightarrow A=\left(-1\right)^{2015}+\left(-1\right)^{2016}+\left(-1\right)^{2017}=-1+1-1=-1\)

Vậy \(A=-1\)