Find the locus of a point whose distance from x-axis is twice the distance from the point (1,-1,2):
(3)
Let the point P(xp,yp,zp) be the required point,
the distance of the point from x-axis is yp2+zp2, The distance from the point (1,-1,2) is
⇒ yp2+zp2=(xp-1)2+(yp+1)2+(zp-2)2⇒xp2-2xp+2yp-4zp+6=0
Therefore, the locus of point P is x2-2x+2y-4z+6=0