If a point lies on yz-plane then what is its x-coordinate?
x-coordinate is the distance of a point from the origin parallel or along the xaxis. To measure the x coordinate, you must move either to the left of the origin or to its right. In case of a point lying on the yz-plane, you do not move to the right or to the left of the origin. Hence x coordinate is 0 for a point on the yz-plane.