Answer:
=x<-7
If they're asking for work, I'd be glad to show.
Use TrianCal to draw a triangle with phi as Great Piramid (minimum perimeter given 2 equal heights) = maximun stability.
NOTE: Phi=(1+√5)/2≈1.62 and acos(1/Phi)≈51.83º
6=3 : 16=6 14=6 that should be right