We multiply the objective function by -1.

For example, minimizing the objective function C = 10x + 6y is equivalent to maximizing the function P = -C = -10x - 6y.

Be careful! When you label your tableaus, you must include the name of the variable that is being maximized. In this case, we would write P (not C) in the tableaus.

We multiply by -1 to get the optimal value. That's because the final tableau will give the optimal value for P = -C (continuing the example from the question above about turning a min LP problem into a max LP problem). To find the optimal value for C, we multiply by -1.