Which one of the following inequalities is redundant for the shaded feasible region (ABCDA) shown below?

Which one of the following inequalities is redundant for the shaded feasible region (ABCDA) shown below?
Solution
A redundant constraint is an unnecessary rule that doesn't form any boundary of the feasible region. Even if removed, the shaded region stays exactly the same.
The four constraints are:
The feasible region is ABCDA with vertices A, B, C, D.
The boundary lines are:
Line 1:
Line 2:
Line 3:
Lines 4: and
Point A (Line 2 meets y-axis):
Put in
Point A
Point B (Line 1 meets Line 2):
From the second equation:
Substituting into the first equation:
Point B
Point C (Line 1 meets x-axis):
Put in
Point C
Point D (Line 2 meets x-axis):
Put in
Point D
Checking if passes through any vertex:
At A :
At B :
At C :
At D :
Constraint 3 doesn't form any edge of the feasible region.
The feasible region ABCDA is completely defined by constraints 1, 2, and 4. Constraint 3 plays no role in forming the boundaries.
Therefore, the inequality is redundant.
The answer is Option 3.
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