Problem 45 - Algebra 1

Question

Graph the function. Describe the domain. $$y=-\frac{3}{x+1}+8$$

Step-by-Step Solution

Answer

The domain of the function y=-3/(x+1)+8 is the set of all real numbers except x=-1. It's graph is a hyperbola with vertical asymptote at x=-1 and horizontal asymptote at y=8.

Step 1: Identify the Domain

Examine the equation for values where the function might be undefined. That's when the denominator is 0. Set x+1=0, solve for x. You'll find x=-1, is excluded from the domain. So, the domain is all real numbers except x=-1.

Step 2: Find Asymptotes

Identify the vertical and horizontal asymptotes of the function. The denominator x+1=0 at x=-1 gives the vertical asymptote. The number added to the rational function, +8, will be the line of the horizontal asymptote, as x approaches infinity.

Step 3: Choose Points and Graph

Select points on either side of the vertical asymptote to plot. Substitute these values into the function to get corresponding y-values. Draw a smooth curve through these points approaching but never touching the asymptotes.

Key Concepts

Domain of Functions

The domain of a function refers to all the input values (x-values) for which the function is defined. For rational functions like \(y = -\frac{3}{x+1} + 8\), it is essential to determine where the function might break down, specifically where the denominator could become zero. In this instance, the denominator is \(x+1\). By setting \(x+1 = 0\), we solve for \(x\) and find that \(x = -1\) causes the denominator to be zero. Thus, the function is undefined at \(x = -1\). Consequently, the domain of the function is all real numbers except \(x = -1\). This means you can plug any real number except \(x = -1\) into the function.

When analyzing domains, always look for restrictions like zeros in the denominator or negative numbers under a square root, as these will guide what \(x\)-values the function can legitimately accept.

Vertical Asymptotes

Vertical asymptotes are lines that the graph of a function approaches but never touches or crosses. They usually occur where the denominator of a rational function equals zero, making the function undefined or tend towards infinity. For the function \(y = -\frac{3}{x+1} + 8\), the vertical asymptote is located where \(x = -1\), as previously determined by setting the denominator equal to zero.

If you were to plot this function, you would notice the graph climbing towards positive or negative infinity as it gets closer to \(x = -1\) from either side. Remember, graphs of rational functions will always have a break at vertical asymptotes, characterized by these never-touch lines.

• Vertical asymptotes represent values that \(x\) can never be.
• They are crucial markers when sketching graphs, indicating where the function will "shoot up" or "drop down" dramatically.

Horizontal Asymptotes

Horizontal asymptotes tell us about the behavior of a graph as \(x\) approaches infinity or negative infinity. They represent the value that a function approaches but does not necessarily reach as \(x\) becomes very large or very small. In our function \(y = -\frac{3}{x+1} + 8\), the horizontal asymptote is \(y = 8\).

This outcome occurs because, as \(x\) grows larger in magnitude, the term \(\frac{3}{x+1}\) becomes insignificantly small (approaching zero), leaving \(y\) to hover around the value of 8. This is a common feature when a constant is added to a rational function, as it sets the baseline for the horizontal asymptote.

• Horizontal asymptotes allow predictions about the end-behavior of a graph.
• Unlike vertical asymptotes, a function can intersect a horizontal asymptote, especially near its center portion.

Understanding horizontal asymptotes provides insight into how functions level off in behavior, giving a "big-picture" view of the graph's dynamics.