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If `a=hati+2hatj+3hatk` and `b=hatixx(axxhati)+hatjxx(axx hatj)+hatk+(a xx hatk)`, then length of b is equal toA. `sqrt(12)`B. `2sqrt(12)`C. `3sqrt(14)`D. `2sqrt(14)` |
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Answer» Correct Answer - B We have , `a=hat(i)+2hat(j)+3hat(k)` `b=hat(i)xx(axxhat(i))+hat(j)xx(axxhat(j))+hat(k)xx(axxhat(k))` Now , `hat(i)xx(axxhat(i))=(hat(i).hat(i))a-(hat(i).a)hat(i)` `=a-a_(1)hat(i)" "["let" (a=a_(1)hat(i)+a_(2)hat(j)+a_(3)hat(k))]` Similarly , `hat(j)xx(axxhat(i))=a-a_(2)hat(j) and hat(k)xx(axxhat(k))` `therefore b=3a-a=2a=2(hat(i)+2hat(j)+3hat(j))` `rArr |b|=sqrt(4+16+36)=sqrt(56)=2sqrt(14)` . |
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