A) \[2/3\]
B) \[3/4\]
C) \[4/5\]
D) \[5/6\]s
Correct Answer: D
Solution :
\[\cos \theta =\left| \frac{{{a}_{1}}{{a}_{2}}+{{b}_{1}}{{b}_{2}}+{{c}_{1}}{{c}_{2}}}{\sqrt{a_{1}^{2}+b_{1}^{2}+c_{1}^{2}}\sqrt{a_{2}^{2}+b_{2}^{2}+c_{2}^{2}}} \right|\] Here, \[{{a}_{1}}=2,\,{{b}_{1}}=-1,\,{{c}_{1}}=1,\,{{d}_{1}}=-1\] and \[{{a}_{2}}=1,{{b}_{2}}=-2,\,{{c}_{2}}=1,\,{{d}_{2}}=2\] \[\therefore \]\[\cos \theta =\left| \frac{(2\times 1)+(-1\times -2)+(1\times 1)}{\sqrt{4+1+1}\sqrt{1+4+1}} \right|\] \[=\left| \frac{2+2+1}{\sqrt{6}\sqrt{6}} \right|\] \[\cos \theta =\left| \frac{5}{6} \right|\]s
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