For what value of ‘a’ the vectors 
and 
are collinear?
Two vectors 
and 
are collinear , if and only if, 
.
Here 
and 
Hence, 
Solving this equality, we get
a=-4
1
For what value of ‘a’ the vectors and are collinear?
Two vectors and are collinear , if and only if, .
Here and
Hence,
Solving this equality, we get
a=-4