ACT Math : Graphing

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #1 : How To Graph A Two Step Inequality

Solve and graph the following inequality:

\(\displaystyle 2x - 7 \geq 6\)

Possible Answers:

\(\displaystyle x=6.5\)

\(\displaystyle x\leq 13\)

\(\displaystyle x\geq13\)

\(\displaystyle x\leq6.5\)

\(\displaystyle x\geq6.5\)

Correct answer:

\(\displaystyle x\geq6.5\)

Explanation:

To solve the inequality, the first step is to add \(\displaystyle 7\) to both sides:

 \(\displaystyle 2x - 7 +7 \geq 6+7\)

\(\displaystyle 2x \geq 13\)

The second step is to divide both sides by \(\displaystyle 2\):

\(\displaystyle \frac{2x}{2} \geq \frac{13}{2}\)

\(\displaystyle x \geq 6.5\)

To graph the inequality, you draw a straight number line. Fill in the numbers from \(\displaystyle 6.5\) to infinity. Infinity can be designated by a ray. Be sure to fill in the number \(\displaystyle 6.5\), since the equation indicated greater than OR equal to.

The graph should look like:

Number_line

Example Question #2 : Graphing

Points \(\displaystyle (3,0)\) and \(\displaystyle (0,3)\) lie on a circle. Which of the following could be the equation of that circle?

Possible Answers:

\(\displaystyle (x+3)^{2}+(y+3)^{2}=9\)

\(\displaystyle (x-3)^{2}+(y+3)^{2}=9\)

\(\displaystyle (x-3)^{2}+(y+3)^{2}=3\)

\(\displaystyle (x-3)^{2}+(y-3)^{2}=3\)

\(\displaystyle (x-3)^{2}+(y-3)^{2}=9\)

Correct answer:

\(\displaystyle (x-3)^{2}+(y-3)^{2}=9\)

Explanation:

If we plug the points \(\displaystyle (3,0)\) and \(\displaystyle (0,3)\) into each equation, we find that these points work only in the equation \(\displaystyle (x-3)^{2}+(y-3)^{2}=9\). This circle has a radius of \(\displaystyle 3\) and is centered at \(\displaystyle (3,3)\).

Example Question #1 : Graphing

Which of the following lines is perpendicular to the line \(\displaystyle y=3x+4\)?

Possible Answers:

\(\displaystyle y=\frac{x}{3}+4\)

\(\displaystyle y=\frac{x}{3}+3\)

\(\displaystyle y=\frac{-x}{3}+2\)

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

\(\displaystyle y=3x+2\)

Correct answer:

\(\displaystyle y=\frac{-x}{3}+2\)

Explanation:

The key here is to look for the line whose slope is the negative reciprocal of the original slope.

In this case, \(\displaystyle \frac{-1}{3}\) is the negative reciprocal of \(\displaystyle 3\).

Therefore, the equation of the line which is perpendicular to the original equation is:

\(\displaystyle y=\frac{-x}{3}+2\)

Example Question #261 : Coordinate Geometry

Let D be the region on the (x,y) coordinate plane that contains the solutions to the following inequalities:

\(\displaystyle x\leq k\), where \(\displaystyle k\) is a positive constant

\(\displaystyle 0\leq y\leq 12x\)

Which of the following expressions, in terms of \(\displaystyle k\), is equivalent to the area of D?

Possible Answers:

\(\displaystyle 8k^2\)

\(\displaystyle 6k^2\)

\(\displaystyle 12k^2\)

\(\displaystyle 3k^2\)

\(\displaystyle 4k^2\)

Correct answer:

\(\displaystyle 6k^2\)

Explanation:

  Inequality_region1

Example Question #2 : How To Graph Inverse Variation

A triangle is made up of the following points: 

\(\displaystyle \left \{ (2,0), (-3,5), (0,4) \right \}\)

What are the points of the inverse triangle?

Possible Answers:

\(\displaystyle \left \{ (0,-2), (-5,3), (-4,0) \right \}\)

\(\displaystyle \left \{ (-2,0), (3,-5), (0,-4) \right \}\)

\(\displaystyle \left \{ (0,2), (5,-3), (4,0) \right \}\)

\(\displaystyle \left \{ (2,0), (3,5), (0,4) \right \}\)

\(\displaystyle \left \{ (-2,0), (-3,-5), (0,-4) \right \}\)

Correct answer:

\(\displaystyle \left \{ (0,2), (5,-3), (4,0) \right \}\)

Explanation:

The inverse of a function has all the same points as the original function, except the x values and y values are reversed. The same rule applies to polygons such as triangles.

Example Question #196 : Coordinate Plane

Electrical power can be generated by wind, and the magnitude of power will depend on the wind speed. A wind speed of \(\displaystyle v\) (in \(\displaystyle \tiny m/s\)) will generate a power of \(\displaystyle v^{2}+4v\) \(\displaystyle watts\). What is the minimum wind speed needed in order to power a device that requires \(\displaystyle 96\) \(\displaystyle watts\)?

Possible Answers:

\(\displaystyle 9 m/s\)

\(\displaystyle 8 m/s\)

\(\displaystyle 3 m/s\)

\(\displaystyle 6 m/s\)

\(\displaystyle 5 m/s\)

Correct answer:

\(\displaystyle 8 m/s\)

Explanation:

The simplest way to solve this problem is to plug all of the answer choices into the provided equation, and see which one results in a power of \(\displaystyle 96\) \(\displaystyle watts\).  

Alternatively, one could set up the equation,

 \(\displaystyle v{^2}+4v-96=0\) and factor, use the quadratic equation, or graph this on a calculator to find the root. 

If we were to factor we would look for factors of c that when added together give us the value in b when we are in the form,

\(\displaystyle ax^2+bx+c\).

In our case \(\displaystyle a=1, b=4, c=-96\). So we need factors of \(\displaystyle -96\) that when added together give us \(\displaystyle 4\).

Thus the following factoring would solve this problem.

\(\displaystyle (v+12)(v-8)=0\)

Then set each binomial equal to zero and solve for v.

\(\displaystyle v+12=0 \rightarrow v=-12\)

\(\displaystyle v-8=0 \rightarrow v=8\)

Since we can't have a negative power our answer is \(\displaystyle {}8 m/s\).

 

Example Question #3 : How To Graph Inverse Variation

Compared to the graph \(\displaystyle y=x^{2}-5\), the graph \(\displaystyle y=(x+4)^{2}-5\) has been shifted:

Possible Answers:

\(\displaystyle 4\) units to the right.

\(\displaystyle 4\) units up.

\(\displaystyle 4\) units to the left.

\(\displaystyle 4\) units down.

\(\displaystyle 5\) units down.

Correct answer:

\(\displaystyle 4\) units to the left.

Explanation:

The \(\displaystyle (+4)\) inside the argument has the effect of shifting the graph \(\displaystyle 4\) units to the left. This can be easily seen by graphing both the original and modified functions on a graphing calculator.  

Example Question #1 : Graphing

The graph of \(\displaystyle y=-4x^{2}+6\) passes through \(\displaystyle (1,2a)\) in the standard \(\displaystyle (x,y)\) coordinate plane. What is the value of \(\displaystyle a\)?

Possible Answers:

\(\displaystyle -1\)

\(\displaystyle 5\)

\(\displaystyle 1\)

\(\displaystyle 0\)

\(\displaystyle 3\)

Correct answer:

\(\displaystyle 1\)

Explanation:

To answer this question, we need to correctly identify where to plug in our given values and solve for \(\displaystyle a\).

Points on a graph are written in coordinate pairs. These pairs show the \(\displaystyle x\) value first and the \(\displaystyle y\) value second. So, for this data:

\(\displaystyle (1,2a)\) means that \(\displaystyle 1\) is the \(\displaystyle x\) value and \(\displaystyle 2a\) is the \(\displaystyle y\) value.

We must now plug in our \(\displaystyle x\) and \(\displaystyle y\) values into the original equation and solve. Therefore:

\(\displaystyle y=-4x^{2}+6\rightarrow 2a=-4(1)^{2}+6\)

We can now begin to solve for \(\displaystyle a\) by adding up the right side and dividing the entire equation by \(\displaystyle 2\).

\(\displaystyle 2a=-4(1)^{2}+6\rightarrow 2a=-4+6\rightarrow2a=2\)

\(\displaystyle 2a=2\rightarrow \frac{2a}{2}=\frac{2}{2}\rightarrow a=1\)

Therefore, the value of \(\displaystyle a\) is \(\displaystyle 1\).

Example Question #2 : Graphing

Coordinate_pair_1

Point A represents a complex number.  Its position is given by which of the following expressions?

Possible Answers:

\(\displaystyle -2+3i\)

\(\displaystyle -2+3\)

\(\displaystyle 3-2i\)

\(\displaystyle 3-2\)

Correct answer:

\(\displaystyle 3-2i\)

Explanation:

Complex numbers can be represented on the coordinate plane by mapping the real part to the x-axis and the imaginary part to the y-axis.  For example, the expression \(\displaystyle a+bi\) can be represented graphically by the point \(\displaystyle (a,b)\).

Here, we are given the graph and asked to write the corresponding expression.

\(\displaystyle 3-2i\) not only correctly identifies the x-coordinate with the real part and the y-coordinate with the imaginary part of the complex number, it also includes the necessary \(\displaystyle i\)

\(\displaystyle 3-2\) correctly identifies the x-coordinate with the real part and the y-coordinate with the imaginary part of the complex number, but fails to include the necessary \(\displaystyle i\).

\(\displaystyle -2+3i\) misidentifies the y-coordinate with the real part and the x-coordinate with the imaginary part of the complex number.

\(\displaystyle -2+3\) misidentifies the y-coordinate with the real part and the x-coordinate with the imaginary part of the complex number.  It also fails to include the necessary \(\displaystyle i\).

Example Question #831 : Act Math

Which of the following graphs represents the expression \(\displaystyle 4-i\)?

Possible Answers:

Coordinate_pair_5

Coordinate_pair_3

Coordinate_pair_2

Coordinate_pair_4

Complex numbers cannot be represented on a coordinate plane.

Correct answer:

Coordinate_pair_4

Explanation:

Complex numbers can be represented on the coordinate plane by mapping the real part to the x-axis and the imaginary part to the y-axis.  For example, the expression \(\displaystyle a+bi\) can be represented graphically by the point \(\displaystyle (a,b)\).

Here, we are given the complex number \(\displaystyle 4-i\) and asked to graph it.  We will represent the real part, \(\displaystyle 4\), on the x-axis, and the imaginary part, \(\displaystyle -i\), on the y-axis.  Note that the coefficient of \(\displaystyle i\) is \(\displaystyle -1\); this is what we will graph on the y-axis.  The correct coordinates are \(\displaystyle (4,-1)\).

 

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