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Vectors a and b are inclined at an angle `theta=120^(@)`. If `|a|=1, |b|=2`, then `[(a+3b)xx(3a+b)]^(2)` is equal to

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Vectors a and b are inclined at an angle `theta=120^(@)`. If `|a|=1, |b|=2`, then `[(a+3b)xx(3a+b)]^(2)` is equal to
A. 190
B. 275
C. 300
D. 192
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Correct Answer - D
Given ,`|a|=1,|b|=2`
`therefore [(a+3b)xx(3a+b)]^2=[0+axxb+9bxxa+0]^2`
`=[-8axxb]^2=64[|a|^2|b|^2sin^2theta]`
`=64[1xx4xxsin^2 120^@]`
`=64xx4xx(3)/(4)=192`
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