(1) The original problem is to get the maximum, so the dual problem is to get the minimum.

For example, in your topic, the original problem is minf, then the dual problem is maxZ.

② The coefficient of the variable in the original problem is the resource coefficient on the right side of the constraint condition in the dual problem.

For example, 2, 3, -5, 1 in the objective function in your topic.

In the dual problem, it is located on the right side of the constraint.

Inversion of constraint matrix of original problem and dual problem. (that is, the matrix formed by the coefficient before the left variable in the constraint condition)

The original question is 1 1 -3 1.

2 0 2 - 1

0 1 1 1

In duality, it is12 0.

1 0 1

3 2 1

③ The constraint of the original problem is ≥, and the variable of the dual problem is ≤

If the variable of the original problem is ≥, then the constraint of the dual problem is ≥.

For example, in your topic, in the original question, X 1≤0, then in the dual question, the first constraint is also ≤ type (you have a question about the answer).

I hope my answer is helpful ~ ~ ~