The equation of locus of a point where distance from the y-axis is equal to its distance from the point A(2,1,-1) is-
y2−2y−4x+2z+6=0
Let the variable point be P(x,y,z).
Its distance from Y−axis=√x2+z2
Its distance from A=√(x−2)2+(y−1)2+(z+1)2
Given √x+z2=√(x−2)2+(y−1)2+(z+1)2⇒y2−2y−4x+2z+6=0