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Which one of the following represents the correct feasible region determined by the following constraints

xy5x - y \geq 5, 5x5y165x - 5y \leq 16

Solution

Correct Option: 1
  1. For the line xy=5x - y = 5 (passes through (5,0)(5,0) and (0,5)(0,-5)):
    • Inequality: xy5x - y \ge 5
    • Testing (0,0)(0,0): 005    050 - 0 \ge 5 \implies 0 \ge 5 (False).
    • This means the region must be on the side away from the origin. Looking at the line passing through (5,0)(5,0), the origin is to its upper-left. So "away from the origin" means shading downward/lower-right.
  2. For the line 5x5y=165x - 5y = 16 (passes through (16/5,0)(16/5, 0) and (0,16/5)(0, -16/5)):
    • Inequality: 5x5y165x - 5y \le 16
    • Testing (0,0)(0,0): 0016    0160 - 0 \le 16 \implies 0 \le 16 (True).
    • This means the region must be on the side containing the origin. Looking at this upper line, the origin is to its upper-left. So "towards the origin" means shading upward/upper-left.

Conclusion:

  • Graph 3 shades the region between the two lines.
  • Graph 1 shades the regions running outwards: below the lower line (xy5x - y \ge 5) and above the upper line (5x5y165x - 5y \le 16).

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