Consider the set of eight vectors
V={ai+bj+ck}:a,b,c ϵ{−1,1}. Three non - coplanar vectors can be chosen from V in 2p ways, Then p is
Given 8 vectors are (1,1,1),(-1,-1,-1,);(-1,1,1),(1,-1,-1,);(1,-1,1), (-1,1,-1);(1,1,-1,),(-1,-1,1)
These are 4 diagonals of a cube and their opposites. For non coplanar vectors first we select 3 groups of diagonals and its opposite in 4C3 ways. Then one vector from each group can be selected in 2×2×2 ways.
∴Total ways=4C3×2×2×2=32=25∴p=5