Browse Questions

# The line $\overrightarrow r=\hat i+2\hat j-\hat k+\lambda(2\hat i-\hat k)$ is $\perp$ to which axis?

$\begin {array} {1 1} (A)\;X-axis & \quad (B)\;Y-axis \\ (C)\;Z-axis & \quad (D)\;\text{ None of the axes} \end {array}$

Toolbox:
• Two lines are $\perp$ if the dot product of their D.R. is =0
Direction ratio (D.R.) of the line is $\overrightarrow b=(1,0,-1)$
D.R. of $Y-axis$ is $(0,1,0)$.
$\therefore$ The line is $\perp$ to $Y-axis$ since $(1,0,-1).(0,1,0)=0$