x1 =  0.00 +0.00i
x2 = -0.63 +0.36i
x3 = -0.63 -0.36i
x4 =  0.00 +0.72i
x5 =  0.00 -0.72i
x6 =  0.63 +0.36i
x7 =  0.63 -0.36i