Absolute Value and Order - GRE Quantitative Reasoning
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What is the solution set of $|x|\ge a$ when $a<0$?
What is the solution set of $|x|\ge a$ when $a<0$?
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All real numbers. For negative a, |x|>=0 is always greater than or equal to a, so all reals satisfy.
All real numbers. For negative a, |x|>=0 is always greater than or equal to a, so all reals satisfy.
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What is the ordering rule comparing $|a|$ and $|b|$ using squares?
What is the ordering rule comparing $|a|$ and $|b|$ using squares?
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$|a|<|b|\iff a^2<b^2$. Squaring both sides preserves the inequality since squares equal the squares of absolutes and are monotonic for non-negative values.
$|a|<|b|\iff a^2<b^2$. Squaring both sides preserves the inequality since squares equal the squares of absolutes and are monotonic for non-negative values.
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What is the solution set of the inequality $|x+2|\ge 4$?
What is the solution set of the inequality $|x+2|\ge 4$?
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$x\le -6$ or $x\ge 2$. Solving |x+2|>=4 splits into x+2 <= -4 or x+2 >=4, subtracting 2.
$x\le -6$ or $x\ge 2$. Solving |x+2|>=4 splits into x+2 <= -4 or x+2 >=4, subtracting 2.
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What is the solution set of the inequality $|2x+1|\le 5$?
What is the solution set of the inequality $|2x+1|\le 5$?
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$-3\le x\le 2$. Solving |2x+1|<=5 gives -5 <= 2x+1 <=5, subtract 1 then divide by 2.
$-3\le x\le 2$. Solving |2x+1|<=5 gives -5 <= 2x+1 <=5, subtract 1 then divide by 2.
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What is the solution set of the inequality $|x-3|<2$?
What is the solution set of the inequality $|x-3|<2$?
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$1<x<5$. Solving |x-3|<2 expands to -2 < x-3 < 2, adding 3 to all parts.
$1<x<5$. Solving |x-3|<2 expands to -2 < x-3 < 2, adding 3 to all parts.
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Which is larger: $|x-1|$ or $|x-4|$ when $x=0$?
Which is larger: $|x-1|$ or $|x-4|$ when $x=0$?
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$|0-4|$ is larger. At x=0, distance to 4 is 4, greater than distance to 1 which is 1.
$|0-4|$ is larger. At x=0, distance to 4 is 4, greater than distance to 1 which is 1.
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Which is larger: $|2-9|$ or $|2-6|$?
Which is larger: $|2-9|$ or $|2-6|$?
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$|2-9|=7$ is larger. Distance from 2 to 9 is 7, exceeding distance to 6 which is 4.
$|2-9|=7$ is larger. Distance from 2 to 9 is 7, exceeding distance to 6 which is 4.
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Which is larger: $-\frac{3}{2}$ or $\left| -\frac{5}{4} \right|$?
Which is larger: $-\frac{3}{2}$ or $\left| -\frac{5}{4} \right|$?
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$\left| -\frac{5}{4} \right|=\frac{5}{4}$ is larger. Absolute value turns -5/4 positive to 1.25, which is greater than -1.5.
$\left| -\frac{5}{4} \right|=\frac{5}{4}$ is larger. Absolute value turns -5/4 positive to 1.25, which is greater than -1.5.
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Which is larger: $|-7|$ or $|-5|$?
Which is larger: $|-7|$ or $|-5|$?
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$|-7|$ is larger. Larger magnitude negative input to absolute value yields larger output, as 7>5.
$|-7|$ is larger. Larger magnitude negative input to absolute value yields larger output, as 7>5.
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Which is larger: $-3$ or $|-4|$?
Which is larger: $-3$ or $|-4|$?
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$|-4|=4$ is larger. Absolute value makes |-4| positive 4, which exceeds -3 on the number line.
$|-4|=4$ is larger. Absolute value makes |-4| positive 4, which exceeds -3 on the number line.
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Identify the correct order from least to greatest: $-2,\ | -3 |,\ 1$.
Identify the correct order from least to greatest: $-2,\ | -3 |,\ 1$.
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$-2<1<|-3|$. Ordering -2 (negative), then 1 (positive), then 3 from | -3 |.
$-2<1<|-3|$. Ordering -2 (negative), then 1 (positive), then 3 from | -3 |.
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What identity relates absolute value to a square root for real $x$?
What identity relates absolute value to a square root for real $x$?
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$|x|=\sqrt{x^2}$. The square root of x squared yields the non-negative root, matching the absolute value.
$|x|=\sqrt{x^2}$. The square root of x squared yields the non-negative root, matching the absolute value.
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Identify the correct order from least to greatest: $|-1|,\ -\frac{3}{2},\ \frac{4}{3}$.
Identify the correct order from least to greatest: $|-1|,\ -\frac{3}{2},\ \frac{4}{3}$.
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$-\frac{3}{2}<|-1|<\frac{4}{3}$. Ordering starts with negative -1.5, then 1 from | -1 |, then positive 1.333.
$-\frac{3}{2}<|-1|<\frac{4}{3}$. Ordering starts with negative -1.5, then 1 from | -1 |, then positive 1.333.
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What is the definition of absolute value $|x|$ written as a piecewise function?
What is the definition of absolute value $|x|$ written as a piecewise function?
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$|x|=\begin{cases}x,&x\ge 0\\-x,&x<0\end{cases}$. The absolute value function returns the non-negative value by taking x when x is non-negative and its negation when x is negative.
$|x|=\begin{cases}x,&x\ge 0\\-x,&x<0\end{cases}$. The absolute value function returns the non-negative value by taking x when x is non-negative and its negation when x is negative.
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What is the distance interpretation of $|a-b|$ on the number line?
What is the distance interpretation of $|a-b|$ on the number line?
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$|a-b|$ is the distance between $a$ and $b$. On the number line, the absolute difference |a-b| measures the positive distance separating points a and b.
$|a-b|$ is the distance between $a$ and $b$. On the number line, the absolute difference |a-b| measures the positive distance separating points a and b.
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What is the largest possible value of $|x|$ when $x$ ranges over all real numbers?
What is the largest possible value of $|x|$ when $x$ ranges over all real numbers?
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No largest value; $|x|$ is unbounded above. Since x can be arbitrarily large positive or negative, |x| can exceed any bound with no maximum.
No largest value; $|x|$ is unbounded above. Since x can be arbitrarily large positive or negative, |x| can exceed any bound with no maximum.
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What is the smallest possible value of $|x|$ for real $x$, and when does it occur?
What is the smallest possible value of $|x|$ for real $x$, and when does it occur?
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Minimum is $0$, occurring at $x=0$. The absolute value |x| is always non-negative, reaching its minimum of 0 only when x=0.
Minimum is $0$, occurring at $x=0$. The absolute value |x| is always non-negative, reaching its minimum of 0 only when x=0.
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What inequality is equivalent to $|x|\le a$ for $a>0$?
What inequality is equivalent to $|x|\le a$ for $a>0$?
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$-a\le x\le a$. For positive a, |x|<=a includes all x within or at distance a from 0.
$-a\le x\le a$. For positive a, |x|<=a includes all x within or at distance a from 0.
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What inequality is equivalent to $|x|>a$ for $a>0$?
What inequality is equivalent to $|x|>a$ for $a>0$?
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$x<-a$ or $x>a$. For positive a, |x|>a means x is more than distance a from 0, either left of -a or right of a.
$x<-a$ or $x>a$. For positive a, |x|>a means x is more than distance a from 0, either left of -a or right of a.
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What inequality is equivalent to $|x|\ge a$ for $a>0$?
What inequality is equivalent to $|x|\ge a$ for $a>0$?
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$x\le -a$ or $x\ge a$. For positive a, |x|>=a includes all x at or beyond distance a from 0.
$x\le -a$ or $x\ge a$. For positive a, |x|>=a includes all x at or beyond distance a from 0.
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What is the solution set of $|x|<0$?
What is the solution set of $|x|<0$?
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No solution; empty set. Since |x| is always >=0, it cannot be less than 0, yielding no solutions.
No solution; empty set. Since |x| is always >=0, it cannot be less than 0, yielding no solutions.
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What is the solution set of $|x|\le 0$?
What is the solution set of $|x|\le 0$?
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$x=0$. Since |x|>=0 and equals 0 only at x=0, |x|<=0 holds solely there.
$x=0$. Since |x|>=0 and equals 0 only at x=0, |x|<=0 holds solely there.
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What is the solution set of $|x|>0$?
What is the solution set of $|x|>0$?
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$x\ne 0$. |x|>0 excludes only x=0 where |x|=0, including all other reals.
$x\ne 0$. |x|>0 excludes only x=0 where |x|=0, including all other reals.
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What is the solution set of $|x|<a$ when $a<0$?
What is the solution set of $|x|<a$ when $a<0$?
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No solution; empty set. For negative a, |x|>=0 cannot be less than a negative number, so no solutions.
No solution; empty set. For negative a, |x|>=0 cannot be less than a negative number, so no solutions.
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