Question

A=i+j b=j+k and c=4i+yj+4k are coplanar vectors.determine value of y.

Answer 1

y=1

because for being coplanar vectors one unit vector should be same.
now here i and k are not same in vectorsA,B&C
so for being coplanar vectors j should be same.
since the value of j is 1 in A and B hence the value of j in C is also 1.