Final answer:
The equation x + y = 3 represents a vertical plane that intersects the xy-plane in the line y = 3 - x, z = 0.
Step-by-step explanation:
The equation x + y = 3 represents a vertical plane in three-dimensional space. To understand this, let's consider the equation in terms of the Cartesian coordinate system. The equation can be rearranged as follows: y = 3 - x. This equation represents a straight line in the xy-plane, where the y-coordinate is equal to 3 minus the x-coordinate. In three-dimensional space, this line intersects the xy-plane at the line y = 3 - x, with z = 0.