For point P(a,b,c)
a is along the x-axis, so does not change the distance from the x-axis.
b and c are both the distance from the x-axis.
Therefore, by the Pythagoras theorem, the
distance from P to the x-axis =
- 
multiply the numerators and multiply the denominators
-
× 
=
= -
= - 
(-1,2.5), (0,5), (1,10), (2,20)