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Determine the domain of each function of two variables. $$f(x, y)=\sqrt{y-3 x}$$

Short Answer

Expert verified
The domain is \(\{(x, y) \in \mathbb{R}^2 \mid y \geq 3x\}\).

Step by step solution

01

Identify the function's expression

The function given is \(f(x, y) = \sqrt{y - 3x}\). In this function, the operation to focus on is the square root.
02

Consider the square root function

Recall that the square root function is only defined for non-negative arguments. Therefore, for the function \(f(x, y) = \sqrt{y - 3x}\), the expression inside the square root, \(y - 3x\), must be greater than or equal to zero.
03

Set up the inequality

To find where the function is defined, set up the inequality: \[y - 3x \geq 0\]
04

Solve the inequality for y

Rearrange the inequality to solve for \(y\): \[y \geq 3x\]
05

Write the domain

The domain is the set of all \((x, y)\) pairs such that \(y \geq 3x\). Therefore, the domain in set notation is: \[D = \{(x, y) \in \mathbb{R}^2 \mid y \geq 3x\}\]

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Key Concepts

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

functions of two variables
Functions of two variables can be more challenging than single-variable functions because they involve two inputs. In our exercise, the function is given by: \[ f(x, y) = \sqrt{y - 3x} \]The domain of a function of two variables consists of all the possible pairs \((x, y)\) that make the function valid.
To understand this better:
  • The first variable, \(x\), and the second variable, \(y\), can represent different quantities.
  • In our case, we look at pairs \((x, y)\) that we plug into the function to make sense of it.
For functions involving two variables, the domain is often represented visually as a region in the xy-plane.
square root function
The square root function is a common mathematical function, but it has specific rules. It is denoted by \(\sqrt{a}\), where \(a\) represents the number under the square root.
Key properties to remember:
  • The function \( \sqrt{a} \) is only defined when \(a\) is greater than or equal to 0.
  • If \(a\) is negative, the square root is not a real number.
In the context of the given exercise: \[ f(x, y) = \sqrt{y - 3x} \]This means that the expression inside the square root, \(y - 3x\) must be non-negative, i.e., \(y - 3x \geq 0\).
If we solve this inequality, we find that \(y \geq 3x\).
Thus, for the values of \(x\) and \(y\) that satisfy this condition, our square root function will yield real numbers.
solving inequalities
Solving inequalities is an essential skill in algebra and it enables us to find the range of input values that make an expression true. Here we consider the inequality from our exercise: \[ y - 3x \geq 0 \]To solve this inequality:
  • First, rearrange the inequality to isolate \(y\): \[ y \geq 3x \]
  • This inequality tells us that for every \(x\), \(y\) must be at least three times \(x\).
  • Graphically, this means that the points \((x, y)\) lie on or above the line \(y = 3x\).
The solution to the inequality provides the domain where our function \(f(x, y)\) is defined. In mathematical terms, the domain is:
\[ D = \{ (x, y) \in \mathbb{R}^2 \mid y \geq 3x \} \]
This set notation indicates all pairs \((x, y)\) in the real number plane where \(y\) is greater than or equal to \(3x\).

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