Find the points on z-is which are at distance `sqrt(21)` from the point (1,2,3).

Explanation

Given purpose be `(1,2,3)`.
Let the purpose on Z axis be given as `(0,0,z)`.
The distance between `(1,2,3) and (0,0,z)` is given as,
`sqrt(1^2+2^2+(3-z)^2)=sqrt(21)`
squaring both sides we have a tandecy to get,
`5+(3-z)^2=21`
`z^2-6z-7=0`
by applying factorization we get factors as,
`z=7 and z=-1`
Hence points are`(0,0,7) , (0,0,-1)`