Answer
See below
Work Step by Step
Given: $v_1=(1,-1,2)\\
v_2=(-2,-4,2)$
We can notice that $-2v_1=-2(1,-1,2)=(-2,2,-4)=v_2$
Obtain $av_1+(-2v_1)\\
=av_1-2bv_1\\
=(a-2b)v_1\\
\rightarrow v \in span \{v_1,v_2\}\\
\rightarrow v \in span \{v_1\}$
Hence, span $\{v_1,v_2\} \subset$ span $\{v_1\}$
Since $v=av_1 \in$ span $\{v_1\}$
$\rightarrow v \in span \{v_1,v_2\}$
$\rightarrow span\{v_1\} =\in span \{v_1,v_2\}$
Geometrically span $\{v_1,v_2\}=$ span $\{v_1\}$ is a line passing through the origin with direction $v_1$
