A) 0
B) 5
C) 15
D) none of these
Correct Answer: A
Solution :
Since, the angle between the vectors is \[{{60}^{o}}\] \[\therefore \] \[\vec{a}.\vec{b}=|\vec{a}||\vec{b}|cos{{60}^{o}}\] \[=1.1.\frac{1}{2}\] \[\left( \therefore \,|\vec{a}|=|\vec{b}|=1 \right)\] \[=\frac{1}{2}\] ?(i) Now, \[(2\vec{a}-3\vec{b}).(4\vec{a}+\vec{b})\] \[=8\vec{a}.\vec{a}+2\vec{a}.\vec{b}-12\vec{a}.\vec{b}-3\vec{b}.\vec{b}\] \[=8(1)-10\vec{a}.\vec{b}-3(1)\] \[[\because \,\,\vec{a}.\vec{a}=1]\] \[=5-10\left( \frac{1}{2} \right)\] [from (i)] \[=0\]You need to login to perform this action.
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