A) 0
B) 2
C) 4
D) 6
Correct Answer: D
Solution :
\[\mathbf{a}\,.\,\mathbf{b}=\,|\mathbf{a}|\,|\mathbf{b}|\cos \theta \]; But \[|\mathbf{a}\times \mathbf{b}|\,=\,|\mathbf{a}|\,|\mathbf{b}|\,\sin \theta \] \[\Rightarrow \sin \theta =\frac{|\mathbf{a}\times \mathbf{b}|}{|\mathbf{a}|\,|\mathbf{b}|}=\frac{4}{5}\Rightarrow \cos \theta =\frac{3}{5}\] Therefore, \[\mathbf{a}\,.\,\mathbf{b}=2\times 5\times \frac{3}{5}=6.\]You need to login to perform this action.
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