Question

Difficulty: MediumSystems of Linear Inequalities in Two Variables
{y2x+4y<12x+2\begin{cases} y \geq -2x + 4 \\ y < \frac{1}{2}x + 2 \end{cases}

Which of the following ordered pairs (x,y)(x, y) is a solution to the system of inequalities above?

  1. (1,2)(1, 2)Answer
  2. B
    (0,1)(0, -1)
  3. C
    (2,3)(2, 3)
  4. D
    (0,3)(0, 3)

Answer

The ordered pair (1,2)(1, 2) is a solution to the system of inequalities.
Substituting the coordinates of the point stating (1,2)(1, 2) into the system of inequalities produces two true statements: 22(1)+42 \geq -2(1) + 4 simplifies to 222 \geq 2, which is true; and 2<12(1)+22 < \frac{1}{2}(1) + 2 simplifies to 2<2.52 < 2.5, which is also true. Therefore, the ordered pair (1,2)(1, 2) is a solution to the system.

Step-by-Step Solution

1
Substitute the coordinates of each option into the first inequality, y2x+4y \geq -2x + 4.
For (1,2)(1, 2), 222 \geq 2 (True). For (0,1)(0, -1), 14-1 \geq 4 (False). For (2,3)(2, 3), 303 \geq 0 (True). For (0,3)(0, 3), 343 \geq 4 (False).
To determine which ordered pairs satisfy the first inequality.
2
Substitute the coordinates of the remaining candidate pairs, (1,2)(1, 2) and (2,3)(2, 3), into the second inequality, y<12x+2y < \frac{1}{2}x + 2.
For (1,2)(1, 2), 2<2.52 < 2.5 (True). For (2,3)(2, 3), 3<33 < 3 (False).
To determine which of the remaining candidates also satisfies the second inequality.
3
Identify the ordered pair that satisfies both inequalities in the system.
Only (1,2)(1, 2) satisfies both inequalities.
An ordered pair is a solution to a system of inequalities if and only if it satisfies all inequalities in the system.

Key Concept

Verifying solutions to a system of linear inequalities by substitution.
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