Omnipotent Data

　　 established a book friend group, 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 below.

　　 Hmm... everyone, please listen to the question! It's time to test whether you are a master student!

　　………………

　　 There is a homogeneous linear equation system below

　　X1+X2+2X3-X4=0

　　2X1+X2+X3-X4=0

　　 2X1+2X2+X3+2X4=0

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

　　 Welcome everyone to join the top academic exchange group! ! A warm welcome! !