Question

The vector $5\hat{i}+2\hat{j}-l\hat{k}$ is perpendicular to the vector $3\hat{i}+\hat{j}+2\hat{k}$ for $l=$

• A. $1$
• B. $4.7$
• C. $6.3$
• D. $8.5$

Answer 1

The correct option is D $8.5$

$(5\hat{i}+2\hat{j}-l\hat{k}).(3\hat{i}+\hat{j}+2\hat{k})=0$

$\therefore \overrightarrow{A}\perp \overrightarrow{B}=$ then $\overrightarrow{A}.\overrightarrow{B}=0$

$=15+2-2l=0$

$=17-2l=0$

$\frac{17}{2}=l$

$l=8.5$