Chapter 2: Problem 81
each function has a graph with an endpoint (a translation of the point (0,0) .) Enter each into your calculator in an appropriate viewing window, and, using your knowledge of the graph of \(y=\sqrt{x}\), determine the domain and range of the function. (Hint: Locate the endpoint.) $$y=10 \sqrt{x-20}+5$$
Short Answer
Expert verified
Domain: \([20, \infty)\), Range: \([5, \infty)\).
Step by step solution
01
Understand the base function
The base function in question is the square root function, given by \( y = \sqrt{x} \). The graph of this function starts at the point (0,0), and is defined for all \( x \geq 0 \). The graph is only in the first quadrant of the coordinate plane.
02
Analyze the Transformation
The given function is \( y = 10\sqrt{x - 20} + 5 \). This is a transformation of the base function \( y = \sqrt{x} \). The transformation \( x - 20 \) shifts the graph 20 units to the right, and the transformation \( +5 \) shifts the graph 5 units upward. Additionally, the coefficient 10 vertically stretches the graph.
03
Determine the Endpoint
The expression under the square root \( x - 20 \) must be non-negative, meaning \( x \geq 20 \). Thus, the endpoint of the function \( y = 10\sqrt{x - 20} + 5 \) will be at \( x = 20 \). Plugging \( x = 20 \) into the function gives \( y = 10\sqrt{0} + 5 = 5 \). Therefore, the endpoint is at (20, 5).
04
Identify the Domain
Since the square root function \( \sqrt{x - 20} \) is defined for \( x \geq 20 \), the domain of the given function \( y = 10\sqrt{x - 20} + 5 \) is \( x \geq 20 \). In interval notation, this is \([20, \infty)\).
05
Identify the Range
The smallest value of \( y \) occurs at the endpoint where \( y = 5 \). As \( x \) increases beyond \( x = 20 \), the value of \( y = 10\sqrt{x - 20} + 5 \) can increase without bound because the square root function gradually increases. Hence, the range is \( y \geq 5 \). In interval notation, this is \([5, \infty)\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Function Transformations
Function transformations help us understand how the graph of a function changes with modifications. Essentially, these transformations can alter the position, size, or shape of a graph.
- **Translation**: A function can be shifted horizontally or vertically. In the function \( y = 10 \sqrt{x - 20} + 5 \), the entire graph is moved 20 units to the right (due to \( x - 20 \)) and 5 units up (due to \( +5 \)). This means the original starting point \((0,0)\) of \( y = \sqrt{x} \) is now at \((20, 5)\).
- **Scaling**: The coefficient before the square root, 10, is a vertical stretch. It makes the graph steeper, meaning for each value of \( x \), \( y \) increases faster than in the unscaled base function.
Domain and Range
In any function, the domain and range are critical. The domain refers to all possible input values (or \( x \)-values) for which the function is defined.
- The domain of \( y = 10\sqrt{x - 20} + 5 \) is based on the expression inside the square root, \( x - 20 \). Since the square root is only defined for non-negative values, \( x \) must be 20 or greater. Thus, the domain is \([20, \infty)\).
- Since the function's starting \( y \)-value is 5, found at the endpoint \((20, 5)\), and \( y \) increases as \( x \) increases, the range is \([5, \infty)\). The graph can rise indefinitely beyond 5.
Square Root Function
The square root function, denoted as \( y = \sqrt{x} \), provides a basic framework for understanding other, more complex functions.
- Its graph starts from the point \((0,0)\), where \( x \geq 0 \), and increases gradually. This creates a distinct curved line in the positive quadrant of the graph.
- The transformation shifts the start to \((20,5)\), and each transformation element alters the way this curve behaves (through translation and stretching).
- The square root's natural non-linearity means that although the change is subtle at first, \( y \) increases more rapidly as \( x \) goes further from the initial starting point.