x²+x+1=0

\(\Leftrightarrow\left(x^2+x+\dfrac{1}{4}\right)+\dfrac{3}{4}=0\)

\(\Leftrightarrow\left(x+\dfrac{1}{2}\right)^2+\dfrac{3}{4}=0\)

\(\Rightarrow x\in\varnothing\)

\(\Rightarrow A=x^n+\dfrac{1}{x^n}\in\varnothing\)

\(2x^2+2y^2-4x+2y-17\)

\(=\left(2x^2-4x+2\right)+\left(2y^2+2y\right)-19\)

\(=2\left(x-1\right)^2+2\left(y^2+y\right)-19\)    \(\left(1\right)\)

Thay x=3;y=-2 ta có:

\(\left(1\right)=2\left(3-1\right)^2+2\left(2^2-2\right)-19\)

\(=2.2^2+2.2-19\)

\(=8+4-19\)

\(=-7\)