A) ? 13
B) ? 10
C) 13
D) 10
Correct Answer: A
Solution :
\[{{(\mathbf{a}+\mathbf{b}+\mathbf{c})}^{2}}=0\] Þ \[|\mathbf{a}{{|}^{2}}+|\mathbf{b}{{|}^{2}}+|\mathbf{c}{{|}^{2}}+2\,\mathbf{a}.\mathbf{b}+2\,\mathbf{b}.\mathbf{c}+2\,\mathbf{c}.\mathbf{a}=0\] Þ \[9+1+16+2(\mathbf{a}.\mathbf{b}+\mathbf{b}.\mathbf{c}+\mathbf{c}.\mathbf{a})=0\] Þ \[\mathbf{a}.\mathbf{b}+\mathbf{b}.\mathbf{c}+\mathbf{c}.\mathbf{a}=-\frac{26}{2}=-13.\]
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