When does an inequality produce a vertical boundary and when a horizontal boundary?
Conditions
- The inequality is in an xy-coordinate system.
- The boundary is determined by replacing the inequality with equality.
Reasoning, step by step
- Identify the variable being restricted in the inequality.
- If only x is restricted, the boundary is a vertical line .
- If only y is restricted, the boundary is a horizontal line .
Example
The narrator says, "X equals three is basically a vertical line," and later, "whenever y is equal to a number, it's going to be a horizontal line as opposed to a vertical line."
Common misconceptions
- Assuming that all inequalities produce diagonal lines.
- Confusing the roles of x and y in determining the boundary orientation.
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Related questions
For an x-inequality, shade to the right if x is greater than the boundary value ( or ), and shade to the left if x is less than the boundary value ( or ).
Conditions: The inequality restricts x.; The boundary is a vertical line .
To graph , first draw a horizontal boundary line at . Make the line solid because the inequality includes equality.
Conditions: The inequality restricts only one variable (y).; The inequality is non-strict (≤).
The boundary line is solid because the inequality includes equality. Since x can be less than or equal to -2, the points on the line are part of the solution set.
Conditions: The inequality is non-strict (≤).; The boundary line is .
The region above is shaded because the inequality requires the y-coordinate to be greater than -4. On a standard coordinate plane, larger y-values are located above the horizontal line .
Conditions: The inequality restricts y.; The boundary is a horizontal line .
The boundary line is dashed because the inequality is strict. Since x is greater than 3 but not equal to 3, the points on the line are excluded from the solution set.
Conditions: The inequality is strict (>).; The boundary line is .
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