Showing vector is perpendicular to the plane

[disturbed123]

if A, B, C are vectors from origin to the points A, B, C show that the following is perpendicular to the plane ABC: (AxB) + (BxC) + (CxA)



I am having trouble setting up the problem. I can't understand the vector A, B, C. is vector A = Ai + Aj + Ak? and so on?

 

[disturbed123]

Sorry for this post found out how to solve it.