Lời giải:
Ta có:
\(\left\{\begin{matrix} \sqrt[3]{x^3-7}+y^2-2y+3=0\\ x^2+x^2y^2-2y=0\end{matrix}\right.\)
\(\Leftrightarrow \left\{\begin{matrix} \sqrt[3]{x^3-7}+2+(y^2-2y+1)=0\\ x^2(y^2+1)=2y\end{matrix}\right.\)
\(\Leftrightarrow \left\{\begin{matrix} \frac{x^3+1}{\sqrt[3]{(x^3-7)^2}+2\sqrt[3]{x^3-7}+4}+(y-1)^2=0(1)\\ x^2=\frac{2y}{y^2+1}(2)\end{matrix}\right.\)
Từ \((2)\Rightarrow 1-x^2=\frac{y^2+1-2y}{y^2+1}\Leftrightarrow (1-x)(1+x)=\frac{(y-1)^2}{y^2+1}\)
Thay vào (1):
\(\frac{x^3+1}{\sqrt[3]{(x^3-7)^2}+2\sqrt[3]{x^3-7}+4}+(1-x)(1+x)(y^2+1)=0\)
\(\Leftrightarrow (x+1)\left[\frac{x^2-x+1}{\sqrt[3]{(x^3-7)^2}+2\sqrt[3]{x^3-7}+4}+(1-x)(y^2+1)\right]=0\)
+) Nếu \(x+1=0\Rightarrow x=-1\Rightarrow y=1\) (thay vào)
+) Nếu biểu thức trong ngoặc lớn bằng $0$
\(\Rightarrow (x-1)(y^2+1)=\frac{x^2-x+1}{\sqrt[3]{(x^3-7)^2}+2\sqrt[3]{x^3-7}+4}>0\)
\(\Rightarrow x>1\) \(\Rightarrow x^2>1\) hay \(\frac{2y}{y^2+1}>1\) hay \(0>(y-1)^2\) (vô lý)
Vậy hpt có nghiệm duy nhất \((x,y)=(-1,1)\)
\(\Rightarrow Q=x^{2008}+y^{2008}=(-1)^{2008}+1^{2008}=2\)
