find the locus of a point which moves such that its distance from the origin is three times its distance from x-axis??

Assume a general point P ( h , k) 
So the distance from the origin O  to P = $\sqrt{h^2 +k^2}$
And this distance is three times the distance from x-axis .

As the distance of P form x-axis is k , so we have
$\sqrt{h^2 +k^2}$ = 3k
Or h² + k² = 9k²
Or h² = 8k²
Or x² = 8y²  ( replacing (h,k) by (x,y))
So the locus is a straight line if you do the square root of the above equation.
x = $\pm 2\sqrt{2}y$
And y = $\pm \frac{x}{2\sqrt{2}}$