Exercise 1 Page 803

Let's look at the given figure. We know that AD⊥l and ABCDEFGH is a cube.

We will determine whether the given statement is true, false, or cannot be determined.

Looking at the figure, we can see that points A, B, C, and D lie in plane M. Since each vertex of square ABCD lies in plane M, square ABCD also lies in plane M. Therefore, the statement is true.