A) ? 5
B) ? 4
C) 4
D) 5
Correct Answer: C
Solution :
\[\mathbf{a}\,.\mathbf{b}=aa\cos 120{}^\circ \], \[\left\{ \because \,|\mathbf{a}|\,=\,|\mathbf{b}|\,=a\,(\text{say}) \right\}\] \[\Rightarrow -8=-\frac{{{a}^{2}}}{2}\Rightarrow a=4\] (Negative sign does not occur in module).You need to login to perform this action.
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