Chapter 7: Problem 33
For each function, calculate the third-order partials a. \(f_{\text {rry }}\), b. \(f_{x y x}\), and \(c\). fyrr. $$f(x, y)=x^{4} y^{3}-e^{2 x}$$
Short Answer
Expert verified
a. 36x^2y^2, b. 36x^2y^2, c. 24x^3y.
Step by step solution
01
Find First-Order Partial Derivatives
First, calculate the partial derivatives of the given function with respect to each variable. The partial derivative with respect to \(x\) is:\[ f_x = \frac{\partial}{\partial x} (x^4 y^3 - e^{2x}) = 4x^3 y^3 - 2e^{2x} \]The partial derivative with respect to \(y\) is:\[ f_y = \frac{\partial}{\partial y} (x^4 y^3 - e^{2x}) = 3x^4 y^2 \]
02
Find Second-Order Partial Derivatives
Now, calculate the second-order partial derivatives from the first-order derivatives.For second-order derivative with respect to \(x\) and \(y\):- \[ f_{xy} = \frac{\partial}{\partial y} (f_x) = \frac{\partial}{\partial y} (4x^3 y^3 - 2e^{2x}) = 12x^3 y^2 \]- \[ f_{yx} = \frac{\partial}{\partial x} (f_y) = \frac{\partial}{\partial x} (3x^4 y^2) = 12x^3 y^2 \]
03
Find Third-Order Partial Derivatives (f_{rry})
Here, we interpret \(r\) as \(x\) since no "r" variable is used in the given function. Thus, \(f_{rry} = f_{xxy}\).Calculate \(f_{rry}:\)\[ f_{rry} = f_{xxy} = \frac{\partial}{\partial x} (f_{xy}) = \frac{\partial}{\partial x} (12x^3 y^2) = 36x^2 y^2 \]
04
Find Third-Order Partial Derivatives (f_{xyx})
Determine \(f_{xyx}\) from second-order and subsequent first-order derivatives.Calculate \(f_{xyx}:\)\[ f_{xyx} = \frac{\partial}{\partial x} (f_{xy}) = \frac{\partial}{\partial x} (12x^3 y^2) = 36x^2 y^2 \]
05
Clarify misunderstood terms (fyrr)
For \(fyrr\), we interpret it as \(f_{yyx}\) since only \(x\) and \(y\) are variables in the function.Calculate \(f_{yyx}:\)- Find \(f_{yy}:\)\[ f_{yy} = \frac{\partial}{\partial y} (f_{y}) = \frac{\partial}{\partial y} (3x^4 y^2) = 6x^4 y \]- Then calculate \(f_{yyx}:\)\[ f_{yyx} = \frac{\partial}{\partial x} (f_{yy}) = \frac{\partial}{\partial x} (6x^4 y) = 24x^3 y \]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Third-Order Derivatives
Third-order derivatives are a step beyond second-order derivatives in calculus, providing the rate of change of the rate of change, taken twice. In simpler terms, they illustrate how the curvature or slope of a function's surface is changing. To find a third-order partial derivative, you begin with calculating first-order derivatives, then second-order, and finally apply the derivative operator once more.
The process implies:
The process implies:
- Calculating first-order partial derivatives (rate of change w.r.t. a single variable).
- Obtaining second-order derivatives based on the first (rates of change of the first-order rate of changes).
- Finally, determining third-order derivatives which capture how these second-order rates change over another variable.
Mathematical Functions
Mathematical functions are expressions that describe a relationship between inputs (often called variables) and outputs. In calculus, they're typically written in the form of an equation y = f(x), where x is the input and y is the output. Functions can also involve multiple variables, which are crucial when dealing with partial derivatives, as seen in the exercise where we have a function of two variables, x and y: \( f(x, y) = x^4 y^3 - e^{2x} \).
Functions serve several purposes:
Functions serve several purposes:
- They demonstrate how changing one quantity affects another.
- They are foundational in developing mathematical models for real-world phenomena.
- Understanding the nature of a function helps in many areas, such as predicting outcomes and analyzing trends.
Calculus
Calculus is a branch of mathematics that studies how things change. It's divided into differential calculus and integral calculus. Differential calculus is the focus here, involving the concept of the derivative. A derivative shows how a function's output value changes based on its input value. When dealing with multi-variable functions, we deal with partial derivatives, which look at how a function changes as one variable changes while others are kept constant.
The steps to address a function with partial derivatives are:
The steps to address a function with partial derivatives are:
- Identify the variables involved.
- Compute the partial derivatives with respect to each of these variables.
- Use these derivatives to find higher-order derivatives if needed.