Write the plane $y + 2z = 1$ in a parametric form I'm asked to write the plane 
$$y + 2z = 1$$
in a parametric form.
I know how to do this with variables like 
$$ax + by + cz = d$$ 
but the lack of an $x$-variable stumps me. How should I go about doing it? 

Since $x$ does not appear in the equation $y+2z=1$, $x$ is simply independent of the values of $y$ and the corresponding $z$. We can thus use any other variables to parametrize $x$. For instance, $t:=x$.
Then we first parametrize $y$ or $z$. Here, we let $u=y$. Since $y$ and $z$ are dependent of each other, $z$ can be parametrize in terms of $u$, which is $\displaystyle z=\frac{1-u}2$.
Thus the possible parametrization is 
$$(t,u,\frac{1-u}2), t,u\in\Bbb{R}$$
