suppose is basis, then there is no such that av1+bv2+cv3=0 unless a,b,c =0
is T a basis?
since V1 and V2 are in V hence d(v1+v2)= dv1+dv2
then we have (a+d)v1+(b+d)v2+cv3=0
clearly if a+d=0, then a need not to be 0 it could be -d