If $X= \{ 4^n-3n-1:n \in N\}$ and $Y=\{9(n-1):n \in N\}$. Where $N$ is the set of natural numbers , then $X \cup Y$ is equal to

$\begin{array}{1 1}(A)\;N \\ (B)\;Y-X \\(C)\;X \\(D)\;Y \end{array}$

X = {$4^n - 3n - 1$}
$\; \;\;=\{ 0, 9, 5, 4, . . . . \}$
$Y = \{9 (n-1)\}$
$\;\;\; = \{0, 9, 18, 27, . ...\}$
$\therefore X\; U \;Y = Y$
edited Nov 6