18 In triangle ABC (Fig 10 18), which of the following is not true:
(A) AB + BC + CA = 0
uuur
uuuur
uuur
r
(B) AB
BC
AC
0
+
−
=
uuur
uuur
uuur
r
(C) AB
BC
CA
0
+
−
=
uuur
uuur
uuur
r
(D) AB
CB
CA
0
−
+
=
uuur
uuur
uuur
r
19 If 
aand
rb
r
 are two collinear vectors, then which of the following are incorrect:
(A)
,  for  some scalar 
b
= λa
λ
r
r
(B) a
= ±b
r
r
(C) the respective components of 
aand
rb
r
 are not proportional
(D) both the vectors 
aand
rb
r
 have same direction, but different magnitudes