Chapter 1: Problem 12
Sketch the graph of each function. Do not use a graphing calculator. (Assume the largest possible domain.) $$ y=\exp (-x) $$
Short Answer
Expert verified
The graph is a decreasing exponential curve with a y-intercept at (0, 1) and a horizontal asymptote at y=0.
Step by step solution
01
Understanding the Function
The function given is \( y = \exp(-x) \), which is the exponential function with base \( e \) and a negative exponent. This characteristic leads to the graph having a certain behavior: as the exponent \( -x \) increases, the overall value of \( y \) decreases.
02
Identify Domain and Range
For the function \( y = \exp(-x) \), the domain consists of all real numbers \( x \). This means you can substitute any real number into \( x \) and still have a defined output. The range of the function is all positive real numbers \( y > 0 \) because an exponential function always outputs a positive number.
03
Analyze Intercepts
To find any intercepts, set \( x = 0 \). This gives \( y = \exp(0) = 1 \). Hence, the y-intercept is \( (0, 1) \). There is no x-intercept because the function never touches the x-axis; it's always positive.
04
Determine Asymptotic Behavior
An asymptote is a line that the graph approaches but never touches. For \( y = \exp(-x) \), as \( x \to \, \infty \), the function approaches \( y = 0 \) but never quite gets there, so \( y = 0 \) (the x-axis) is a horizontal asymptote.
05
Sketch the Graph
Use the information gathered to sketch the graph. It starts from the point \( (0, 1) \), rapidly decreases as \( x \) increases and gets closer but never reaches the x-axis as \( y = 0 \). As \( x \) becomes more negative, \( y \) increases exponentially, making the graph rise steeply to the left.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Graph Sketching
Sketching the graph of exponential functions like \( y = \exp(-x) \) may sound tricky, but when broken down into parts, it becomes much simpler. The function itself is a classic example of an exponential decay graph because of its negative exponent. Let’s break it down step by step.
- Starting Point: The first important coordinate is the y-intercept where \( x = 0 \). At this point, \( y = \exp(0) = 1 \). This means the graph crosses the y-axis at (0, 1).
- Slope Direction: As \( x \) increases to the positive, the graph starts high and rapidly moves downward toward the x-axis.
- Rising Left: As \( x \) becomes negative, the graph actually rises. This is because the negative exponent becomes less negative, thus increasing \( y \) steeply.
Asymptotes
Asymptotes are invisible lines that your function’s graph will get very close to, but never actually touch or cross. In the case of \( y = \exp(-x) \), understanding asymptotes helps you see the limits and bounds of a function. Here's what to look for:
- Horizontal Asymptote: The x-axis, or \( y = 0 \), acts as a horizontal asymptote for this function. As \( x \to \infty \), \( y \) approaches zero. It never quite reaches the x-axis, emphasizing the persistent positivity of the exponential function.
- Graph Behavior Near Asymptote: The graph descends toward this horizontal line but eternally floats just above it. A characteristic of decay functions is such asymptotic behavior, where the values of the function keep halving as they near the horizontal boundary.
Function Behavior
Understanding the behavior of \( y = \exp(-x) \) is essential to grasp how exponential functions work, especially with negative exponents. Observably, this function expresses exponential decay. Let's break down the key behavioral traits:
- Decay: This function diminishes rapidly as \( x \) becomes positive. The higher the value of \( x \), the smaller \( y \) becomes, drawing close to zero without reaching it.
- No X-Intercepts: Notice that it never touches or crosses the x-axis. This reiterates the fact that the function's output never dips into negative numbers.
- Exponential Growth in Negative Direction: Interestingly, for negative \( x \), the function value rises. As \( x \) becomes more negative, the exponent decreases negatively, causing multiplication of a quickly enlarging number.