Two subspaces 
and 
of 
are orthogonal if the dot product 
for all vectors 
and all 
.
Orthogonal Subspaces
See also
Dot Product, SubspaceExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Orthogonal Subspaces." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/OrthogonalSubspaces.html