a)
[tex]\it 9x^2+y^2+42x-4y+55=2|_{-2} \Rightarrow 9x^2+y^2+42x-4y+53=0\Rightarrow\\ \\ \Rightarrow 9x^2+y^2+42x-4y+49+4=0\Rightarrow \\ \\ \Rightarrow (9x^2+42x+49)+(y^2-4+4)=0\Rightarrow(3x+7)^2+(y-2)^2=0\Rightarrow [/tex]
[tex]\it \Rightarrow \begin{cases}\it 3x+7=0 \Rightarrow 3x=-7 \Rightarrow x=-\dfrac{7}{3} \Rightarrow x=-2,(3)\\ \\ \it y-2=0 \Rightarrow y=2\end{cases}[/tex]
