When graphing a linear inequality, when can you NOT use (0, 0) as a test point to determine which side of a boundary line to shade?

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  when (0, 0) is on the boundary line

Step-by-step explanation:

Any test point you use to determine shading must not lie on the boundary line. You need a test point that will make the inequality true or false. That is, it must give a result a > b or a ≥ b, where a ≠ b. A point on the boundary line will give a = b, so is not helpful.

If the test point gives "true", then it lies in the shaded area. If it gives "false," then the other side of the line is shaded.

(0, 0) cannot be used as a test point when it lies on the boundary line.