I set up a book friend group, and the group number is: 7-0-6-8-0-0-0-5-8-9

There will be a problem when joining a group, and the problem is below.

Well...... Everyone, please listen to the question! It's time to test whether you are a top student!

..................

Underneath 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 the coefficient matrix of this system of equations is the answer to joining the group!!

Welcome everyone to join the top academic exchange group!!Warm welcome!!

The "Universal Data" book friend group is here!! I hit it in my hand, please wait a while,

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