Official Guide Explanation:
Problem Solving #21

Background

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Solution and Metadata

Question: 21
Page: 64
Difficulty: 5 (Moderate)
Category 1: Geometry > Coordinate Geometry > Slope
Category 2: Geometry > Coordinate Geometry > Other

Explanation: (A) and (B) are the equations for the axes, and since the shaded region is bounded by the axes on the left and bottom, those two choices are eliminated. x = 1 is the boundary on the right side: vertical lines are always x= an integer. It isn't nearly as obvious what the equation of the diagonal line is, but it may be clearer that (D) isn't it. x - y = 0 is the same as x = y, and x = y is a diagonal line that goes through the origin (when x = 0 and y = 0) and moves up and to the right from there. Thus, (D) is the odd man out, and the correct answer.

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