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Math Help - How to graph inequality on a plane

  1. #1
    Junior Member
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    How to graph inequality on a plane

    The part that gets me is the plane thing.

    X + Y < 1

    If x is 0 then Y is 0, -1, -2, -3 and so on right?

    If y is 0 then the same applies for X =0, -1,-2, -3 and so on?

    Please correct me if I am wrong.

    Therefore How do I graph this? And what sets of numbers should I use?

    00 for both won't work???
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  2. #2
    MHF Contributor

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    Yes, the values you give are correct but the graph has to include non integers, rational and irrational numbers as well.

    The graph of the equation, y= x+1, is a straight line. On that line, when x= 0, y= 1 and when y= 0, x= -1. The graph of y= x+1 is the straight line through (0, 1) and (-1, 0).

    The reason you should graph that line first is that it forms the boundary of the points that satisfy y< x+ 1. Obviously that line divides all of R^2 into two subsets. The points that satisfy y< x+ 1 is one of the two subsets on either side of the line. Choose a point on each side of the line to determine which side satifies the inequality.

    Also, because this is y< x+ 1, rather than y\le x+1, you don't want to include the line itself in the graph. One way to indicate that is to use a dashed line rather than a full line.
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