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Sketching a Graph In Exercises \(59-74\) , sketch the graph of the equation using extrema, intercepts, symmetry, and asymptotes. Then use a graphing utility to verify your result. $$ y=3+\frac{2}{x} $$

Short Answer

Expert verified
This function's graph does not cross any axis (it lacks x and y intercepts), has no extrema, possesses a vertical asymptote at \(x = 0\) and a horizontal asymptote at \(y = 3\), and displays no symmetry. While the graph can be difficult to sketch by hand, using a graphing tool will correct small inaccuracies.

Step by step solution

01

Intercept

Determine where the function crosses the x and y axes. For the y-intercept, determine y when \(x = 0\), which is undefined in this case. That implies there's no y-intercept. For the x-intercept, set y to zero and solve for x: \(0 = 3+ \frac{2}{x}\) which also has no real solution.
02

Extrema

Extrema are local maximums and minimums of the function. The function \(y = 3 + \frac{2}{x}\) is decreasing for \(x > 0\) and increasing for \(x < 0\), but it has no turning points (no local maximum or minimum).
03

Symmetry

Test the function for symmetry: If the function is equal to its original equations when \(x\) is replaced by \(-x\), it's even, showing symmetry around the y-axis. If the function's sign is negated when \(x\) is replaced by \(-x\), then it's odd, showing rotational symmetry around the origin. In this function, neither condition is met, so it's neither even nor odd.
04

Asymptotes

Find any asymptotes: vertical asymptotes occur where the function is undefined. Our function is undefined when \(x = 0\), so that is a vertical asymptote. A horizontal asymptote is found by loooking at the behavior of the function as \(x\) approaches \(\pm \infty\). This function approaches \(y = 3\), so we have horizontal asymptote at \(y = 3\).
05

Sketching

After identifying the characteristics above, sketch the graph taking everything into account. You should get a curve that approaches each of your asymptotes without touching them - also because there are no intercept, the graph won't touch either axis.
06

Verification with a graphing tool

Plug the function into a graphing tool as a final step to check your work and adjust your graph as necessary.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Intercepts of Functions
When we talk about intercepts of a function, we are referring to the points where the graph crosses the x-axis and y-axis. For the y-intercept, determine the y-value when the x-value is zero. In our case, substituting \(x = 0\) into the equation \(y = 3 + \frac{2}{x}\) is not possible because the expression becomes undefined. This means there is no y-intercept for this function.

For the x-intercept, set the whole function equal to zero and solve for x. Doing this for our function, we get \(0 = 3 + \frac{2}{x}\). Solving this equation yields no real solution, indicating that the graph does not cross the x-axis either. This is a unique situation where the graph has neither x nor y intercepts.
Function Extrema
Extrema in functions refer to the maximum and minimum values on a graph. These can be either local (occurring at a particular point in a restricted region) or global (over the entire domain of the function). For our function \(y = 3 + \frac{2}{x}\), determining its extrema involves examining its derivative to find critical points.

This function behaves differently on different intervals: it decreases for x-values greater than zero and increases for x-values less than zero. However, it doesn't have any turning points where the graph changes from increasing to decreasing, or vice versa. This means the graph of this function has no local maxima or minima.
Symmetry in Functions
In graph sketching, symmetry can help simplify the plotting process. The two main types of symmetry are even and odd functions. A function is even if replacing \(x\) with \(-x\) doesn't change the function; it looks the same on either side of the y-axis. Similarly, a function is odd if replacing \(x\) with \(-x\) results in the negative of the original function.

Our function \(y = 3 + \frac{2}{x}\) does not satisfy either condition. Substituting \(-x\) into our function gives a different result than the original, confirming it has no symmetry about the origin or the y-axis. This information helps in understanding the overall shape and behavior of the graph.
Asymptotes of Functions
Asymptotes are lines that a graph approaches but never actually touches. Understanding asymptotes gives valuable information about the behavior of a function as the inputs become very large or small.

For our function \(y = 3 + \frac{2}{x}\), we have a vertical asymptote at \(x = 0\) because the function is undefined at this point. As \(x\) gets closer to zero, the value of \(y\) shoots up or down dramatically, depending on the side of zero that \(x\) approaches.

The horizontal asymptote is found by examining the function as \(x\) approaches infinity. In this function, as \(x\) gets very large or very small, \(\frac{2}{x}\) approaches zero, leading \(y\) to approach 3. Hence, there is a horizontal asymptote at \(y = 3\). This horizontal asymptote tells us that no matter how large \(x\) becomes, the value of the function will get very close to 3.

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