Before you start, make sure you know: Second-degree equations (High School Year 1 (semesters 1 and 2))
At a street market (tianguis), the scale at the produce stand should give bags of $1{,}000$ g, but it is allowed to be off by up to $20$ g, either above or below. What are the limit weights of an acceptable bag? To answer, it helps to know that an absolute value equation hides two equations at once. At the end of the page we come back to the scale.
Definition and the basic case $|ax+b|=k$
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Solve the following linear equation with absolute value: $|3x - 5| = 7$
Solve the following linear equation with absolute value:
Setting up a distance problem means translating "at distance $d$ from $a$" as $|x-a|=d$. Two points always come out, one on each side of $a$: $x=a+d$ and $x=a-d$.
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Find the numbers whose distance to the number $4$ on the number line is exactly $9$. Set up and solve the corresponding absolute value equation.
Find the numbers whose distance to the number $4$ on the number line is exactly $9$. Set up and solve the corresponding absolute value equation.
Solve the following equation by equating the absolute value of a quadratic expression to the absolute value of a linear expression: $|x^2 - 5x + 4| = |2x - 6|$
Solve the following equation by equating the absolute value of a quadratic expression to the absolute value of a linear expression:
The graph of $|x^2-5x|$ is the parabola with the part below the $x$-axis "folded" upward. The line $y=6$ cuts it at four points: those are the solutions of $|x^2-5x|=6$.
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Find the values of $x$ that satisfy the following quadratic equation with absolute value: $|x^2 - 9| = 0$
Find the values of $x$ that satisfy the following quadratic equation with absolute value:
A particle oscillates around an equilibrium point. Its position $x$ at certain critical moments satisfies the equation $|x^2 - 10| = 3x$. Find the exact positions $x$…
A particle oscillates around an equilibrium point. Its position $x$ at certain critical moments satisfies the equation $|x^2 - 10| = 3x$. Find the exact positions $x$ where this occurs, making sure to discard invalid solutions.
When there is a fraction inside the absolute value, it is solved the same way with one extra step: the denominator cannot equal zero. The values that make it zero are excluded from the start.
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Solve the following rational equation with absolute value: $\left| \frac{x+2}{x-1} \right| = 3$
Solve the following rational equation with absolute value:
If $x^2$ and $|x|$ both appear in the equation, there are two paths.
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Find the solutions to the following equation by making a suitable substitution or distinguishing cases according to the sign of $x$: $x^2 - 4|x| - 5 = 0$
Find the solutions to the following equation by making a suitable substitution or distinguishing cases according to the sign of $x$:
Find the solutions to the equation by dividing the number line into intervals according to the roots of the arguments of the absolute values: $|x - 2| + |x + 3| = 7$
Find the solutions to the equation by dividing the number line into intervals according to the roots of the arguments of the absolute values:
A robotic arm moves along a linear rail. Its distance to two beacons located at positions $x=0$ and $x=10$ must satisfy the constraint given by the equation…
A robotic arm moves along a linear rail. Its distance to two beacons located at positions $x=0$ and $x=10$ must satisfy the constraint given by the equation $2|x| - |x - 10| = 5$. Find the exact $x$ coordinates where the robot can stop.
With the graph you can count solutions without solving. The solutions of $|f(x)|=k$ are the crossings of the graph of $y=|f(x)|$ with the horizontal line $y=k$. Move $k$ in the figure.
The graph of $|x^2-4x+3|$ has a "W" shape: the original parabola has its vertex at $(2,-1)$ and crosses the axis at $x=1$ and $x=3$, and the lower part is reflected, forming a peak at $(2,1)$.
Value of $k$
Solutions
$k<0$
none
$k=0$
two ($x=1$, $x=3$)
$0
four
$k=1$
three (right at the peak)
$k>1$
two
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Determine the value of the parameter $k$ for which the equation $|x^2 - 4x + 3| = k$ has exactly three distinct real solutions. In the figure you have the graph of…
Determine the value of the parameter $k$ for which the equation $|x^2 - 4x + 3| = k$ has exactly three distinct real solutions.
In the figure you have the graph of $f(x)=|x^2-4x+3|$. Use it to reason how many solutions the equation has depending on the height of the horizontal line $y=k$, and justify the value of $k$ with calculations.
A tolerance is the maximum difference allowed from an ideal value, and it is written with absolute value: $|\text{value}-\text{ideal}|=\text{tolerance}$ gives the two limits.
Back to the start: the scale at the tianguis. $|m-1000|=20$ gives $m=1{,}020$ g or $m=980$ g. A bag is acceptable between $980$ g and $1{,}020$ g.
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A machine cuts steel cables for a suspension bridge. The length $L$ (in meters) of a cable is considered acceptable if it satisfies the tolerance equation…
A machine cuts steel cables for a suspension bridge. The length $L$ (in meters) of a cable is considered acceptable if it satisfies the tolerance equation $|2L - 150| = 1.5$. Calculate the maximum and minimum acceptable lengths for the cable.
In an economic model, the deviation of the price $P$ of a share from its benchmark value of $2\,400$ pesos is proportional to the price itself, modeled by the equation…
In an economic model, the deviation of the price $P$ of a share from its benchmark value of $2\,400$ pesos is proportional to the price itself, modeled by the equation $|P - 2\,400| = \frac{P}{5}$. Calculate the exact prices that satisfy this condition.
During a chemistry experiment, the margin of error in measuring the pH of a buffer solution is given by the equation $|2p - 14| = p - 4$, where $p$ is the pH value.…
During a chemistry experiment, the margin of error in measuring the pH of a buffer solution is given by the equation $|2p - 14| = p - 4$, where $p$ is the pH value. Calculate the possible values of $p$ and discard any that lack physical or mathematical meaning in this equation.
And the support of a camping tent, with a beam at a certain height, is solved with intervals just like in the previous section:
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The entrance profile of a modern-design tent is modeled by the equation $y = |x - 4| + |x - 8|$, where $x$ and $y$ are in meters. To place a horizontal support beam at a…
The entrance profile of a modern-design tent is modeled by the equation $y = |x - 4| + |x - 8|$, where $x$ and $y$ are in meters. To place a horizontal support beam at a height of $y = 6$ meters, solve the equation $|x - 4| + |x - 8| = 6$ to find the $x$ coordinates of the ends of the support.