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x2+x+1=0
\(\Leftrightarrow\left(x^2+x+\dfrac{1}{4}\right)+\dfrac{3}{4}=0\)
\(\Leftrightarrow\left(x+\dfrac{1}{2}\right)^2+\dfrac{3}{4}=0\)
\(\Rightarrow x\in\varnothing\)
\(\Rightarrow A=x^n+\dfrac{1}{x^n}\in\varnothing\)
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\(2x^2+2y^2-4x+2y-17\)
\(=\left(2x^2-4x+2\right)+\left(2y^2+2y\right)-19\)
\(=2\left(x-1\right)^2+2\left(y^2+y\right)-19\) \(\left(1\right)\)
Thay x=3;y=-2 ta có:
\(\left(1\right)=2\left(3-1\right)^2+2\left(2^2-2\right)-19\)
\(=2.2^2+2.2-19\)
\(=8+4-19\)
\(=-7\)
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