Question

The position vectors of two points A and B are $i+j-k$ and $2i-j+k$ respectively. Then $\left|AB\right|=$

• A. $2$
• B. $4$
• C. $3$
• D. $5$

Answer 1

The correct option is C $3$

$A=i+j-k\text{and}B=2i-j+k$
$\therefore AB=(2i-j+k)-(i+j-k)=i-2j+2k$
$\therefore |AB|=\sqrt{1^2+(-2{)}^2+2^2}=\sqrt{9}=3$
Option C is correct.