////////////////////////////////////////////////////////////////
//
//     http://www.planetquantum.com/Solve/Level1/Den13/Page11.txt
//
////////////////////////////////////////////////////////////////

Generator:
(C (^ _Pi 1/2) (Sec 1) 6 7 2)

Problem:
(= (cdot #[[17 72 45 38 50 90 55]
           [16 2 72 98 16 74 83]
           [34 11 45 18 27 97 54]
           [94 56 12 23 87 12 82]
           [13 80 77 89 85 29 11]
           [28 45 91 3 21 81 37]]
         #[[x_1] [x_2] [x_3] [x_4] [x_5] [x_6] [x_7]])
   #[[18] [50] [81] [57] [17] [68]])

Solution:
(= #[[x_1] [x_2] [x_3] [x_4] [x_5] [x_6] [x_7]]
   #[[-98222197350]
     [-46941685761]
     [30519297672]
     [-55615485505]
     [89949479112]
     [-24737724954]
     [63973092254]])