Here are the correct completions for your sentences:
- x-axis: the horizontal axis in a coordinate plane
- y-axis: the vertical axis in a coordinate plane
- x-coordinate: the horizontal position of a point on the coordinate plane
- y-coordinate: the vertical position of a point on the coordinate plane
So, the completed sentences are:
- x-axis: the horizontal axis in a coordinate plane
- y-axis: the vertical axis in a coordinate plane
- x-coordinate: the horizontal position of a point on the coordinate plane
- y-coordinate: the vertical position of a point on the coordinate plane