The first floor is right. In fact, it doesn't matter how you draw it, but if it is really horizontal and vertical as you think, it is only one of many situations, and other situations are oblique. We study the general laws in mathematics, not the results under special conditions, although the results are correct in this special inclusion.

Some people say, "both point F and point O are fixed, that is, a right-angled side is fixed and inclined." This statement only conforms to the number of the first question. "