Chapter 2: Problem 29
The function \(f:(-\infty,-1] \rightarrow\left(0, e^{5}\right]\) defined by, \(f(x)=e^{x^{3}-3 x+2}\) is (A) Many one and onto (B) Many one and into (C) One-one and onto (D) One-one and into
Short Answer
Expert verified
(D) One-one and into
Step by step solution
01
Define the Function and Domain
We start with the function given as \( f(x) = e^{x^3 - 3x + 2} \) with the domain \( (-\infty, -1] \). The range is \( (0, e^5] \).
02
Check if the Function is One-One
To check if the function is one-one, we need to determine if \( f(x_1) = f(x_2) \) implies \( x_1 = x_2 \). Consider the derivative \( f'(x) = e^{x^3 - 3x + 2} \cdot (3x^2 - 3) \). Evaluate this derivative on the interval \( (-\infty, -1] \) to see if it's monotonic (always increasing or always decreasing).
03
Determine Monotonicity
Calculate \( f'(x) = e^{x^3 - 3x + 2} \cdot (3x^2 - 3) \). Notice \( 3x^2 - 3 = 3(x^2 - 1) \). Within the domain \( (-\infty, -1] \), \( x^2 > 1 \), so \( 3x^2 - 3 > 0 \). This means \( f'(x) > 0 \), indicating that the function is strictly increasing and hence one-one.
04
Check if the Function is Onto
Since \( f(x) = e^{x^3 - 3x + 2} \) ranges from more than 0 but equal to or less than \( e^5 \), and given that the domain is \( (-\infty, -1] \), we need to verify that every value in the range \((0, e^5]\) is achievable. For \( f(-1) = e^{(-1)^3 - 3(-1) + 2} = e^4\), the maximum value of \( e^5 \) is not reached, hence making the function 'into'.
05
Final Verification and Conclusion
Combine the results from previous steps: The function is one-one (strictly increasing) and does not map onto every possible value \((0, e^5]\) due to limitations when approaching \( e^5 \). Therefore, the function is many one and into.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Derivative Test
The derivative test is a helpful tool in understanding how a function behaves across its domain. It allows us to conclude whether a function is constantly increasing or decreasing by analyzing its derivative. For the function given, \( f(x) = e^{x^3 - 3x + 2} \), the derivative is calculated as: \[ f'(x) = e^{x^3 - 3x + 2} \cdot (3x^2 - 3) \] This derivative is crucial in investigating the function's monotonicity. A derivative test checks if it is positive or negative across the domain. If \( f'(x) > 0 \) throughout the domain \((-\infty, -1]\), then the function is strictly increasing in this interval. Conversely, if \( f'(x) < 0 \), the function would decrease. In this exercise, the derivative is always positive within the domain, hinting at a one-one nature of the function.
Monotonicity
Monotonicity refers to whether a function is consistently increasing or decreasing. This characteristic is significant because it helps determine if a function is one-one or many-one. For the present function \( f(x) = e^{x^3 - 3x + 2}\), we derived that:\[ f'(x) = e^{x^3 - 3x + 2} \cdot (3x^2 - 3) \] To evaluate this, consider the simplifying term \(3(x^2 - 1)\). Within the domain \((-\infty, -1]\), \(x^2 > 1\). Therefore, \(3(x^2 - 1) > 0\). Since the exponential function \(e^{x^3 - 3x + 2}\) is always positive, the product is positive, confirming the function is strictly increasing across the given domain. Knowing this, we understand these increasing functions are also injective or one-one.
Increasing Functions
An increasing function is one whose output grows as the input value increases. For functions like \(f(x) = e^{x^3 - 3x + 2}\), which are strictly increasing on their interval, each input produces a unique output. This is clear from the derivative test: - Since \( f'(x) > 0 \) for all \(x\) in the domain \((-\infty, -1]\), the function is said to be strictly increasing.- Such functions are injective, meaning they assign a unique output to each input, ensuring there are no repeated values in the range.By understanding whether a function is increasing, one can categorize it as one-one, which is essential in this exercise for establishing the nature of the function.
Domain and Range in Functions
Understanding the domain and range is essential in grasping a function's capabilities and limitations. The domain refers to all possible input values, while the range indicates all potential outputs. For this function, \(f(x) = e^{x^3 - 3x + 2}\), the stated domain is \((-\infty, -1]\), and the intended range is \((0, e^5]\).- **Domain:** Informs which \(x\) values are permissible for evaluating the function. Here it includes all numbers less than or equal to \(-1\).- **Range:** Describes the values that \(f(x)\) can assume. Through calculation, it achieves values more than 0 up to, but not surpassing, \(e^5\).To check if a function is onto, we investigate whether every value in the range can be paired with a corresponding \(x\). In this example, since outputs achieve values close to but not equaling the maximum \(e^5\), the function fits the description of a function that is into rather than onto. This distinction is crucial for correctly interpreting the function's nature.