Linear subspaces

The set $\left\{ \begin{bmatrix} x \\ y \\ z \end{bmatrix} \in \mathbb{R}^3: z \geq 0 \right\}$

The plane generated by $\begin{bmatrix} 1 \\ 3 \\ 9 \end{bmatrix}$ and $\begin{bmatrix} 0 \\ 2 \\ 4 \end{bmatrix}$ in $\mathbb{R}^3$

The graph of the function $y = 4x^3$ in $\mathbb{R}^2$.

The graph of the function $y = 8x$ in $\mathbb{R}^2$.

Points on the circle of radius $1$ centered at the origin in $\mathbb{R}^2$.