Question

If the projection of $2\hat{i}+4\hat{j}-2\hat{k}$ on $\hat{i}+2\hat{j}+\alpha \hat{k}$ is zero. Then, the value of $\alpha$ will be

Answer 1

Answer: 5

$\overrightarrow{a}\cdot \overrightarrow{b}=0$
$\therefore \overrightarrow{a}\cdot \overrightarrow{b}=0$
$\therefore 2\times 1+4\times 2-2\times \alpha =0$
$\therefore \alpha =5$