Find a vector ` vec r` of magnitude `3sqrt(2)` units which makes an angle of `pi/4` and `pi/2` with `y` and z-axis respectively.

Explanation

Let `l, m, n` be the direction cosines of the vector `vec r` and `l = cos α,`
`m = cos β`

`=cos frac{pi}{4}`

`=frac{1}{sqrt{2}}`

And, `n=cos gamma`

`=cos frac{pi}{2}`

`=0`

Also,` |^{2}+m^{2}+n^{2}=1`

`Rightarrow l^{2}+(frac{1}{sqrt{2}})^{2}+0=1`

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