A group of book friends has been established. The group number is: 7-0-6-8-0-0-5-8-9

    there will be a problem when adding a group. The problem is in the following.

    Well Everybody, please listen to the question! It''s time to test if you''re learning to be a bully!

    ………………

    There is a system of homogeneous linear equations

    X1 + x2 + 2x3-x4 = 0

    2x1 + x2 + x3-x4 = 0

    2x1 + 2x2 + X3 + 2x4 = 0

    the rank of coefficient matrix of this equation system is the answer to the group!!

    Welcome to join the top academic exchange group!! a warm welcome!!

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