The questions are on the following picture please add steps

The questions are on the following picture (please add steps to the solution for a,b,c):

PLEASE NOTE: This is a *****************Linear Algebra Problem***************

a) a

A(1,1,-1,-1) , B -(-1,1,1,1) , C(-1,-1,1,1), D(1,-1,-1,-1) , E(1,-1,1,1)

A.B = -2/4 A.C = -4/4 A.D = 2/4 A.E = -2/4

B.C = 2/4 B.D = -4/4 B.E = 0/4

C.D = -2/4 C.E = 2/4

D.E = 0/4

now

compatible - angle is smaller or equal to 60 degree

or X.Y >= 2/4

incompatible angle is greater or equal to 120 degree

X.Y <= -2/4

so a) compatible are

(A,D) , (B,C) ,(C,E)

b)Incompatible

(A,B) , (A,E), (B,D) , (C,D)