14. The range of the projection area of a regular tetrahedron with edge length 1 on a plane is what?
14. (1) For the projection being 1 triangle, the maximum area is 1 equilateral $\triangle$ with a side length of 1, the value is $\frac{\sqrt{3}}{4}$; the minimum occurs when the projections of two points coincide, at this time $S=\frac{\sqrt{2}}{4}$.
(2) When the projection is 1 quadrilateral, the maximum area is $1 \times 1 \times \frac{1}{2}=\frac{1}{2}$. The minimum occurs when it degenerates into 1 triangle.
From the above, the range of values is $\left[\frac{\sqrt{2}}{4}, \frac{1}{2}\right]$.