So Should the i-th slack variable of the primal is not really zero, then the i-th variable of the dual is equivalent to zero. Similarly, Should the j-th slack variable of the dual is not really zero, then the j-th variable on the primal is equal to zero. This carefully https://paxtonpivgq.blogdigy.com/5-simple-techniques-for-linear-programming-assignment-help-40245916