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Math Lesson 15.4.4 - How to Find the Equation of a Reciprocal Graph?

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Welcome to our Math lesson on How to Find the Equation of a Reciprocal Graph?, this is the fourth lesson of our suite of math lessons covering the topic of Reciprocal Graphs, you can find links to the other lessons within this tutorial and access additional Math learning resources below this lesson.

How to Find the Equation of a Reciprocal Graph?

Sometimes we have the graph of a reciprocal function given but not the function's formula. We can find it by following the procedure below:

Step 1: Assume the function's formula to be in the form

y = a/x - h + k

Step 2: Check whether you are able to determine the equations of asymptotes by sight. This is possible if the units are clearly defined (as in all our examples where the units are shown by the squares). If you can find the asymptotes, then you have found the values of h and k in the above formula.

Step 3: After having identified the position of asymptotes, substitute the coordinates of a known point on the graph to find the coefficient a. If the asymptotes cannot be determined by sight, then solve a system of three equations obtained when you substitute the coordinates of three known points of the graph in the general formula above. It is impossible to solve a system of three equations with the concepts explained so far, but you will learn how to solve them in the upcoming topics of this course when dealing with matrices and determinants.

Example 7

Which function is shown in the graph below?

Math Tutorials: Reciprocal Graphs Example

Solution 7

From the figure, it is clearly visible that x = 3 is a vertical asymptote and y = 2 is a horizontal one. Therefore, we have h = 3 and k = 2. Likewise, we can see that the point with coordinates (4, 3) is a point of the graph. Hence, for x = 4, y = 3, h = 3 and k = 2, we have

y = a/x - h + k
3 = a/4 - 3 + 2
3 = a + 2
a = 1

Hence, the equation of the hyperbola shown in the graph is

y = 1/x - 3 + 2

You have reached the end of Math lesson 15.4.4 How to Find the Equation of a Reciprocal Graph?. There are 5 lessons in this physics tutorial covering Reciprocal Graphs, you can access all the lessons from this tutorial below.

More Reciprocal Graphs Lessons and Learning Resources

Types of Graphs Learning Material
Tutorial IDMath Tutorial TitleTutorialVideo
Tutorial
Revision
Notes
Revision
Questions
15.4Reciprocal Graphs
Lesson IDMath Lesson TitleLessonVideo
Lesson
15.4.1The Meaning of the Term "Reciprocal" in Math
15.4.2The Graph of a Reciprocal Function
15.4.3Asymptotes of Reciprocal Graphs
15.4.4How to Find the Equation of a Reciprocal Graph?
15.4.5Determining the Equation of the Symmetry Line of a Reciprocal Graph

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  4. Types of Graphs Practice Questions: Reciprocal Graphs. Test and improve your knowledge of Reciprocal Graphs with example questins and answers
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  6. Continuing learning types of graphs - read our next math tutorial: Exponential Graphs

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