I can't understand the analysis of this problem. Who can explain it in detail in another way?

Deeply understand the definition of matrix multiplication.

If b is the column vector x

Ax=0

What does this mean?

The linear combination of the column vectors of a is equal to 0.

B is column n.

AB=0

Aren't all the linear combinations of the column vectors of N A equal to 0?

This means that the column vectors of A are linearly related.

The above is the analysis when focusing on A.

Similarly, AB=0 represents the linear vector of B, which is linearly related.