Proving Linear Independence: Vectors in R^5 and Their Span

[NeonVomitt]

Suppose that v1,v2,v3 are linearly independent vectors in R^5 and consider the vectors a1,a2,a3 defined by a1=v1+v2-2v3, a2=3v1+v2+4va, and a3=v1+2v2-7v3. Show that at least one of the vectors v1,v2,v3 is not in the span of the vectors a1,a2,a3.

I am kind of confused. Should I somehow reduce row echelon it? But how would I even set that up given this type of format?

Thank you!

 

[lurflurf]

a=T.v
where
T={{1,1,-2},{3,1,4},{1,2,-7}}