Practicing Success
A unit vector perpendicular to the vector $-\hat i+2\hat j+2\hat k$ and making equal angles with X and Y axes can be |
$\frac{1}{3}(2\hat i+2\hat j-\hat k)$ $\frac{1}{3}(2\hat i-2\hat j-\hat k)$ $\frac{1}{3}(2\hat i+2\hat j+\hat k)$ $\frac{1}{3}(2\hat i-2\hat j+\hat k)$ |
$\frac{1}{3}(2\hat i+2\hat j-\hat k)$ |
Let the required vector be $\vec r=l\hat i+m\hat j+n\hat k$ where $l, m, n$ are the direction cosines of $\vec r$ such that $l = m$. It is given that $\vec r$ is perpendicular to $-\hat i + 2\hat + 2\hat k$. Therefore, $\vec r.(-\hat i+2\hat j+2\hat k) =0$ $⇒-l+2m+2n=0$ $⇒l+2n=0$ $[∵l=m]$ $⇒l=-2n$ Now, $l^2+ m^2 + n^2=1⇒ 4n^2 + 4n^2+n^2=1⇒n=±\frac{1}{3}$ $∴l=±\frac{2}{3},m=±\frac{2}{3}$ and $n=±\frac{1}{3}$ Hence, $\vec r=±\frac{1}{3}(2\hat i+2\hat j-\hat k)$ |