1.

If `vec(a)=(hat(i)-2hat(j)+3hat(k)) and vec(b)=(hat(i)-3hat(k))` then `|vec(b)xx 2vec(a)|=?`A. `10sqrt(3)`B. `5sqrt(17)`C. `4sqrt(19)`D. `2sqrt(23)`

Answer» Correct Answer - C
`vec(b)=(hat(i)+0hat(j)-3hat(k))and 2hat(a)=(2hat(i)-4hat(j)+6hat(k))`.
`:. (vec(b)xx2vec(a))=|(hat(i),hat(j) ,hat(k)),(1,0,-3),(2,-4,6)|=(0-12)hat(i)-(6+6)hat(j)+(-4-0)hat(k)`
`=(-12hat(i)-12hat(j)-4hat(k))`.
`:. |vec(b)xx2vec(a)|^(2)={(-12)^(2)+(-12)^(2)+(-4)^(2)}=(144+144+16)=304`.
Hence, `|vec(b)xx2vec(a)|=sqrt(304)=4sqrt(19)`.


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