MCQ
If $a, b, c $ are unit vectors such that $a + b + c = 0,$ then $a\,\,.\,\,b + b\,\,.\,\,c + c\,\,.\,\,a = $
- A$1$
- B$3$
- ✓$-3/2$
- D$3/2$
we get ${a^2} + {b^2} + {c^2} + 2a.b + 2b.c + 2c.a = 0$
==> $|a{|^2} + |b{|^2} + |c{|^2} + 2(a.b + b.c + c.a) = 0$
==> $2(a.b + b.c + c.a) = - 3$ $ \Rightarrow a.b + b.c + c.a = - \frac{3}{2}$.
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