Question

Can a given line be in two planes? In ten planes?

Answer 1

In geometry, the plane and the line are two of the three undefined terms. The other undefined term is the point. They are called as such because they are so basic that you don't really define them. They are used instead to define other terms in geometry. However, you can still describe them.  A plane is described as any flat surface with an area in one dimension only. A line is a series of points that extend infinitely in one direction on both ends.

Yes, a line can be in two planes. Let me give a concrete example. I'm sure a majority, if not everybody, has seen a laptop. You will observe that a laptop has two planes represented by the keyboard and the laptop screen. As shown in the diagram in the attached picture, you can see the two planes intersect and coincide at one line, represented by the one in red. In this case, the line is both in two planes. 

For the second question, the answer is yes. A line can be in ten planes. Suppose you hit an arrow through a series of plastic boards to hit a target. On the right side of the picture, you can see that a line intersects all ten planes.