A) 6
B) 3
C) \[-3\]
D) 5
E) \[-6\]
Correct Answer: E
Solution :
Since, the vector\[8i+aj\]in the direction of the vector\[4i-3j\]. That means both vectors are parallel to each other. By condition of parallel vectors, \[\frac{8}{4}=\frac{a}{-3}\] \[\Rightarrow \] \[a=-6\] Alternative Method Given also, \[|8i+aj|=10\] \[\Rightarrow \] \[\sqrt{64+{{a}^{2}}}=10\] \[\Rightarrow \] \[64+{{a}^{2}}=100\] \[\Rightarrow \] \[{{a}^{2}}=36\] \[\Rightarrow \] \[a=\pm 6\] (here we take (-) ve sign) \[\Rightarrow \] \[a=-6\]
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