MathChapter 4: Linear Inequalities and Graphs
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Prompt
What does AND mean in a compound inequality?
💡Look for overlap.
Answer
A value must satisfy both conditions: use the intersection.
Example\(-2<x\) and \(x\le4\) becomes \(-2<x\le4\).
Prompt
What does OR mean in a compound inequality?
💡Keep either valid part.
Answer
A value must satisfy at least one condition: use the union.
Example\(x<-3\) or \(x\ge2\) gives two rays.
Prompt
What is an intersection?
Answer
The values shared by every solution set.
ExampleThe overlap of \(x>-1\) and \(x<5\) is \(-1<x<5\).
Prompt
What is a union?
Answer
All values belonging to at least one solution set.
ExampleCombine separated rays without filling the gap.
Prompt
How do you solve a chained inequality?
💡Keep the chain balanced.
Answer
Apply each operation to all three parts.
ExampleFrom \(-3<2x+1\le9\), subtract \(1\) everywhere.
Prompt
For \(a>0\), what is \(|E|<a\) equivalent to?
💡Small distance means inside.
Answer
\(-a<E<a\).
Example\(|x|<4\) gives \(-4<x<4\).
Prompt
For \(a>0\), what is \(|E|\le a\) equivalent to?
💡Include boundary distances.
Answer
\(-a\le E\le a\).
Example\(|x|\le3\) gives \(-3\le x\le3\).
Prompt
For \(a>0\), what is \(|E|>a\) equivalent to?
💡Large distance means outside.
Answer
\(E<-a\) or \(E>a\).
Example\(|x|>2\) gives two open rays.
Prompt
For \(a>0\), what is \(|E|\ge a\) equivalent to?
💡Outside includes boundaries.
Answer
\(E\le-a\) or \(E\ge a\).
Example\(|x|\ge5\) includes \(-5\) and \(5\).
Prompt
Why does absolute-value less-than use AND?
💡Distance is bounded on both sides.
Answer
The expression must lie between the two boundary values simultaneously.
ExampleDistance from zero less than \(3\) stays between \(-3\) and \(3\).
Prompt
Why does absolute-value greater-than use OR?
💡Two outside directions.
Answer
The expression may lie beyond either the negative boundary or the positive boundary.
ExampleDistance greater than \(3\) means left of \(-3\) or right of \(3\).
Prompt
What must happen before splitting an absolute-value inequality?
💡Remove outside constants first.
Answer
Isolate the absolute-value expression.
ExampleFrom \(2|x|+1<9\), first obtain \(|x|<4\).
Prompt
What is the solution of \(|E|<0\)?
💡Distance cannot be negative.
Answer
No solution.
ExampleNo real absolute value is strictly below zero.
Prompt
What is the solution of \(|E|\ge0\)?
💡Absolute value is nonnegative.
Answer
All real inputs for which the expression is defined.
Example\(|2x-1|\ge0\) is always true.
Prompt
What is the solution of \(|E|\le0\)?
💡Only zero has distance zero.
Answer
Exactly the values making \(E=0\).
Example\(|x+4|\le0\) gives \(x=-4\).
Prompt
What endpoint mistake commonly occurs with compounds?
💡Carry the original equality status.
Answer
Changing a strict endpoint to closed or an inclusive endpoint to open.
Example\(<\) remains open after adding a number.
Prompt
How do integer restrictions change a compound solution?
💡List them explicitly.
Answer
Filter the real interval to the integers it contains.
Example\(-1<x\le3\) gives integers \(0,1,2,3\).
Prompt
Can an OR inequality simplify to one ray?
💡Take the union.
Answer
Yes, when one branch contains the other.
Example\(x>2\) or \(x>5\) simplifies to \(x>2\).
Prompt
Can an AND inequality have no solution?
💡Take the intersection.
Answer
Yes, when its required intervals do not overlap.
Example\(x<1\) and \(x>4\) is impossible.
Prompt
What is the main SAT check after solving two branches?
💡Inside uses intersection; outside uses union.
Answer
Confirm the connector and endpoint inclusion match the original condition.
ExampleDo not write \(|x|>3\) as \(-3<x<3\).
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