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91Ó°ÊÓ

For each function: a. Evaluate the given expression. b. Find the domain of the function. c. Find the range. [Hint: Use a graphing calculator.] $$ f(x)=\sqrt{x-4} ; \text { find } f(40) $$

Short Answer

Expert verified
f(40) = 6; Domain: [4, ∞); Range: [0, ∞)

Step by step solution

01

Evaluate the Expression

First, substitute the given value into the function.Substitute \( x = 40 \) into the function \( f(x) = \sqrt{x - 4} \). So, \( f(40) = \sqrt{40 - 4} = \sqrt{36} = 6 \).Therefore, \( f(40) = 6 \).
02

Determine the Domain

The domain of a function \( f(x) = \sqrt{x-4} \) consists of all \( x \) values that make the expression under the square root non-negative.That is, \( x - 4 \geq 0 \).Solving this inequality: \( x \geq 4 \).Thus, the domain is all real numbers \( x \) such that \( x \geq 4 \), represented as \([4, \infty)\).
03

Determine the Range Using Graph Analysis

The range of the function \( f(x) = \sqrt{x-4} \), for \( x \geq 4 \), starts at \( f(4) = \sqrt{4 - 4} = \sqrt{0} = 0 \) and can extend upwards to positive infinity.Since \( \sqrt{x-4} \) is always non-negative and increases as \( x \) increases, the range is \([0, \infty)\).Use a graphing calculator to confirm that the graph of \( f(x) \) supports this range.

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Key Concepts

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

Evaluating Expressions
To evaluate an expression for a given function, we replace the variable with a specific value. Consider the function \( f(x) = \sqrt{x-4} \). When we need to find \( f(40) \), we substitute \( x = 40 \) into the function. This leads to the calculation \( f(40) = \sqrt{40 - 4} \).

Simplifying inside the square root gives us \( \sqrt{36} \), which results in 6, since 6 squared is 36. Thus, \( f(40) = 6 \). Evaluating expressions requires careful substitution and simplification to find the right answer.
Domain of a Function
The domain of a function includes all possible input values (\( x \)) that result in a real number output. For the function \( f(x) = \sqrt{x-4} \), we need to ensure that the expression inside the square root remains non-negative. Subtracting 4 from \( x \) should not result in a negative number, which means \( x - 4 \geq 0 \).

Solving this inequality, we find \( x \geq 4 \). Therefore, the domain in interval notation is \([4, \infty)\). When determining a domain, consider any restrictions the function might have, such as not allowing division by zero or taking the square root of a negative number.
Range of a Function
The range of a function is the set of all possible output values. For \( f(x) = \sqrt{x-4} \), as \( x \) starts at 4 and goes to infinity, the output of the function is always non-negative. Let's see why.

When \( x = 4 \), the function evaluates to 0, meaning \( f(4) = \sqrt{4-4} = 0 \). As \( x \) increases, \( \sqrt{x-4} \) becomes larger because you're taking the square root of greater numbers. This results in a range of \([0, \infty)\). Graphing the function can help confirm this range by visually showing that the function's outputs start at 0 and increase without bound as \( x \) grows.

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