The heights of two trees are x and y, where x > y. The tops of the trees are at a distance z apart. If s is the shortest distance between the trees, then what is s2 equal to?
1
x2 + y2 - z2 - 2xy
2
x2 + y2 - z2
3
x2 + y2 + z2 + 2xy
4
z2 - x2 - y2 + 2xy