Algebra 1 : How to graph an absolute value function

Study concepts, example questions & explanations for Algebra 1

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Example Questions

Example Question #1 : How To Graph An Absolute Value Function

Absolute_value

Which of these would most likely be the equation corresponding to the above graph?

Possible Answers:

\(\displaystyle y = |x - 2 | -1\)

\(\displaystyle y = |x - 2 | +1\)

\(\displaystyle y = |x + 2 | -1\)

\(\displaystyle y = |x + 3 |\)

\(\displaystyle y = |x + 2 | +1\)

Correct answer:

\(\displaystyle y = |x - 2 | -1\)

Explanation:

This is an absolute value graph. Its equation takes the form \(\displaystyle y = |x-h|+k\), in which \(\displaystyle h,k\) represent the number of units that the base graph \(\displaystyle y = |x|\) is translated right and up respectively.

 

Since the graph of \(\displaystyle y = |x|\) is translated two units right and one unit down, \(\displaystyle h = 2\) and \(\displaystyle k = -1\), so the equation would be:

\(\displaystyle y = |x-2|+(-1)\)

or 

\(\displaystyle y = |x - 2 | -1\)

Example Question #42 : Functions And Lines

Give the \(\displaystyle x\)-intercept(s) of the graph of the function \(\displaystyle f(x) = 7 - \left | 2x-3 \right |\)

Possible Answers:

The graph has no \(\displaystyle x\)-intercepts.

\(\displaystyle (-5,0) , (2,0)\)

\(\displaystyle (-2,0) , (2,0)\)

\(\displaystyle (-2,0) , (5,0)\)

\(\displaystyle (-5,0) , (5,0)\)

Correct answer:

\(\displaystyle (-2,0) , (5,0)\)

Explanation:

To find the \(\displaystyle x\)-intercept(s) of the graph, set \(\displaystyle f(x) = 0\) and solve for \(\displaystyle x\).

\(\displaystyle f(x) = 7 - \left | 2x-3 \right |\)

\(\displaystyle 0= 7 - \left | 2x-3 \right |\)

\(\displaystyle 0 + \left | 2x-3 \right |= 7 - \left | 2x-3 \right | + \left | 2x-3 \right |\)

\(\displaystyle \left | 2x-3 \right |= 7\)

 

Rewrite this as the compound equation:

\(\displaystyle 2x-3= -7\) or \(\displaystyle 2x-3= 7\)

 

Solve each separately:

\(\displaystyle 2x-3= -7\)

\(\displaystyle 2x-3 + 3 = -7+ 3\)

\(\displaystyle 2x = -4\)

\(\displaystyle 2x \div 2 = -4\div 2\)

\(\displaystyle x = -2\)

 

\(\displaystyle 2x-3= 7\)

\(\displaystyle 2x-3 + 3 = 7+ 3\)

\(\displaystyle 2x = 10\)

\(\displaystyle 2x \div 2 = 10\div 2\)

\(\displaystyle x = 5\)

 

There are two \(\displaystyle x\)-intercepts: \(\displaystyle (-2,0) , (5,0)\)

Example Question #43 : Graphing

Absolute_value

 

Which of these would most likely be the equation corresponding to the above graph?

Possible Answers:

\(\displaystyle y = | x + 6 | - 3\)

\(\displaystyle y = | x - 6 | - 3\)

\(\displaystyle y = | x + 3 | - 6\)

\(\displaystyle y = | x - 3 | - 6\)

\(\displaystyle y = | x - 6 | + 3\)

Correct answer:

\(\displaystyle y = | x + 3 | - 6\)

Explanation:

This is an absolute value graph. Its equation takes the form \(\displaystyle y = |x-h|+k\), in which \(\displaystyle h,k\) represent the number of units that the base graph \(\displaystyle y = |x|\) is translated right and up respectively.

 

Since the graph of \(\displaystyle y = |x|\) is translated three units left and six units down, \(\displaystyle h = -3\) and \(\displaystyle k = -6\).

Plug these values into the general form of the equation:

\(\displaystyle y = |x-(-3)|+(-6)\)

Simplify:

\(\displaystyle y = |x+3|-6\)

Example Question #1 : How To Graph An Absolute Value Function

\(\displaystyle \textup{What is the slope of } y=-4\left | x-2\right | \textup{ when } x=1?\)

Possible Answers:

\(\displaystyle -4\)

\(\displaystyle 4\)

\(\displaystyle -1\)

\(\displaystyle 1\)

\(\displaystyle \textup{It does not exist.}\)

Correct answer:

\(\displaystyle 4\)

Explanation:

\(\displaystyle \textup{When }x=1\textup{ the expression inside the absolute value is negative,} \\\textup{so the function can be written as } y=-4(2-x)=4x-8,\textup{ with a slope of 4.}\\\textup{Plus, the slope changes to -4 when } x>2. \textup{ When } x=2 \textup{ it does not exist.}\)

Example Question #1 : How To Graph An Absolute Value Function

\(\displaystyle \textup{Find the lowest attainable value of }y \textup{ in } y=-4+ \left |4x^2-25 \right |.\)

Possible Answers:

\(\displaystyle -2.5\)

\(\displaystyle -4\)

\(\displaystyle 2\)

\(\displaystyle 0\)

\(\displaystyle 2.5\)

Correct answer:

\(\displaystyle -4\)

Explanation:

\(\displaystyle \\ \left | 4x^2-25\right | \textup{cannot get any lower than zero,}\\\textup{so\textit{ y} cannot get any lower than} -4.\)

Example Question #46 : Functions And Lines

\(\displaystyle \textup{Which is an \textit{x}-intercept of the function } y=\left | -x^2-8x-16\right |-4.\)

Possible Answers:

\(\displaystyle -2\)

\(\displaystyle -4\)

\(\displaystyle 0\)

\(\displaystyle \textup{None of the above.}\)

\(\displaystyle 4\)

Correct answer:

\(\displaystyle -2\)

Explanation:

\(\displaystyle \\ \textup{The function can be simplified as } \\y=\left | -(x+4)^2\right |-4=\left |(x+4)^2\right |-4=(x+4)^2-4.\\\textup{In order to find the \textit{x}-intercecpt, we solve the equation}\\0=(x+4)^2-4 \textup{ which becomes }\\(x+4)=\pm2\textup{ and has solution } -2 \textup{ and } -6.\)

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