1)

If  |a|=3|b|=2,|c|=1 then the value of |a.b+b.c+c.a| is (given that  a+b+c=0 )


A) -7

B) 7

C) 14

D) -14

Answer:

Option B

Explanation:

a+b+c=0

 (a+b+c)2=0

 |a|2+|b|2+|c|2+2(a.b+b.c+c.a)=0

9+4+1+2(a.b+b.c+c.a)=0

 a.b+b.c+c.a=7