How do i calculate point z when given only x y and a distance z is away from the 0,0 point

Question

Example

X = -2

Y = -1

Z = -4

Distance is 4

Calculated from standard formula

D= Sqrroot (X² + Y² + Z²)

Using the above example how would I find Z if it was unknown to me ?

Answer 1

(x,y,z) = (-2.-1, z)

z^2 = 16 given distance from the origin =4

z=+/-4

z= either 4 or -4

unless you meant the distance from (-2,-1,z) to the origin = 4

then

16=4+1+z^2

z^2 = 11

z= +/-sqr11= about 3.3 or -3.3