\(x^2-x-2=0\Rightarrow\left[{}\begin{matrix}x=-1\left(\notin N\right)\\x=2\end{matrix}\right.\)
\(\Rightarrow A=\left\{2\right\}\)
\(B=\left\{1;2;5\right\}\)
a.
\(A\subset B\) (đúng)
b, Đúng
\(A\subset X\subset B\)
\(\Rightarrow X=\left\{2\right\};\left\{1;2\right\};\left\{2;5\right\};\left\{1;2;5\right\}\)