Question

Difficulty: MediumSystems of Linear Inequalities in Two Variables

Consider the system of inequalities below:

3x+y>5x−2y>4\begin{aligned} 3x + y &> 5 \\ x - 2y &> 4 \end{aligned}

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

  1. A
    (3,1)(3, 1)
  2. B
    (2,−1)(2, -1)
  3. (4,−2)(4, -2)Answer
  4. D
    (3,2)(3, 2)

Answer

(4,−2)(4, -2)
The coordinate pair (4,−2)(4, -2) is the correct answer because substituting these values into both inequalities of the system produces true statements: 3(4)+(−2)=10>53(4) + (-2) = 10 > 5 and 4−2(−2)=8>44 - 2(-2) = 8 > 4.

Step-by-Step Solution

1
Substitute the coordinates of the candidate point into the first inequality, 3x+y>53x + y > 5.
For (4,−2)(4, -2), we get 3(4)+(−2)=12−2=103(4) + (-2) = 12 - 2 = 10. Since 10>510 > 5, the first inequality is satisfied.
A coordinate pair must satisfy both inequalities in the system to be a solution.
2
Substitute the coordinates of the candidate point into the second inequality, x−2y>4x - 2y > 4.
For (4,−2)(4, -2), we get 4−2(−2)=4+4=84 - 2(-2) = 4 + 4 = 8. Since 8>48 > 4, the second inequality is also satisfied.
Since both inequalities are true for (4,−2)(4, -2), it is a valid solution to the system.

Key Concept

A coordinate pair (x,y)(x, y) is a solution to a system of linear inequalities if and only if it makes all inequalities in the system true when substituted.
Estimated Time:1m 30s
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