ACT Math : How to graph inverse variation

Study concepts, example questions & explanations for ACT Math

varsity tutors app store varsity tutors android store varsity tutors ibooks store

Example Questions

Example Question #193 : Algebra

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:

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

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

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

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

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

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 #1 : Graphing

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:

\(\displaystyle 5 m/s\)

\(\displaystyle 9 m/s\)

\(\displaystyle 8 m/s\)

\(\displaystyle 3 m/s\)

\(\displaystyle 6 m/s\)

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 #2 : 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 up.

\(\displaystyle 5\) units down.

\(\displaystyle 4\) units down.

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

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

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.  

Learning Tools by Varsity Tutors