Let P(h, k) be a point. Let O(0, 0) be the origin.So, the distance of point P(h, k) from the x-axis is k.∴ OP = 3k⇒ O P2 = ( 3k )2⇒ ( h − 0 )2 + ( k − 0 )2 = ( 3k )2  ⇒ h2 + k2 = 9 k2  ⇒ h2 = 8 k2Hence, the locus of (h, k) is x2 = 8 y2.