Chapter 3: Problem 47
Find the indicated higher-order partial derivatives. Let \(F(x, y, z)=x^{3} y z^{2}-2 x^{2} y z+3 x z-2 y^{3} z .\) Find \(F_{x y z}\)
Short Answer
Expert verified
The higher-order partial derivative \(F_{xyz} = 6x^2 z - 4x\).
Step by step solution
01
Find the First Partial Derivative with respect to x
To find the partial derivative \(F_x\), treat \(y\) and \(z\) as constants. Differentiate \(F(x, y, z)\) with respect to \(x\):\[ F_x = \frac{\partial}{\partial x}(x^{3} y z^{2} - 2x^{2} y z + 3xz - 2y^{3} z) \]- The derivative of \(x^3 y z^2\) with respect to \(x\) is \(3x^2 y z^2\).- The derivative of \(-2x^2 y z\) with respect to \(x\) is \(-4x y z\).- The derivative of \(3xz\) with respect to \(x\) is \(3z\).- The derivative of \(-2y^3 z\) with respect to \(x\) is \(0\) (since \(-2y^3 z\) does not contain \(x\)).So,\[ F_x = 3x^2 y z^2 - 4x y z + 3z \]
02
Find the Second Partial Derivative with respect to y
Now, differentiate \(F_x\) with respect to \(y\):\[ F_{xy} = \frac{\partial}{\partial y}(3x^2 y z^2 - 4x y z + 3z) \]- The derivative of \(3x^2 y z^2\) with respect to \(y\) is \(3x^2 z^2\).- The derivative of \(-4x y z\) with respect to \(y\) is \(-4x z\).- The derivative of \(3z\) with respect to \(y\) is \(0\).Thus,\[ F_{xy} = 3x^2 z^2 - 4x z \]
03
Find the Third Partial Derivative with respect to z
Finally, differentiate \(F_{xy}\) with respect to \(z\):\[ F_{xyz} = \frac{\partial}{\partial z}(3x^2 z^2 - 4x z) \]- The derivative of \(3x^2 z^2\) with respect to \(z\) is \(6x^2 z\).- The derivative of \(-4x z\) with respect to \(z\) is \(-4x\).Therefore,\[ F_{xyz} = 6x^2 z - 4x \]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Understanding Partial Derivatives with Respect to x
A partial derivative with respect to a specific variable, such as \( x \), involves differentiating a function while treating all other variables as constants. In this process, we're focusing on how the function changes along the \( x \) direction, considering \( y \) and \( z \) as fixed.
Let's apply this to the function \( F(x, y, z) = x^3 y z^2 - 2x^2 y z + 3xz - 2y^3 z \):
Understanding how the function changes with \( x \) helps see its impact along the \( x \)-axis. This is the first step in relating partial derivatives in multivariable functions.
Let's apply this to the function \( F(x, y, z) = x^3 y z^2 - 2x^2 y z + 3xz - 2y^3 z \):
- For the term \( x^3 y z^2 \), we differentiate with respect to \( x \), considering \( y z^2 \) as a constant multiplier. The derivative is \( 3x^2 y z^2 \).
- The term \( -2x^2 y z \) becomes \( -4x y z \) after differentiation, where \( 2y z \) is treated as a constant.
- The \( 3xz \) term simplifies to \( 3z \) after differentiating, as \( z \) is constant: we only focus on \( x \).
- Finally, \( -2y^3 z \) does not contain \( x \), resulting in a derivative of \( 0 \).
Understanding how the function changes with \( x \) helps see its impact along the \( x \)-axis. This is the first step in relating partial derivatives in multivariable functions.
Exploring Partial Derivatives with Respect to y
To find the partial derivative with respect to \( y \), we treat all other variables as constants, just as we did with \( x \). We aim to understand how changes in \( y \) alone impact the function.
Starting from the partial derivative \( F_x = 3x^2 y z^2 - 4x y z + 3z \), we differentiate with respect to \( y \):
This step highlights how variations in \( y \) influence the function, holding \( x \) and \( z \) steady. This insight can reveal patterns that arise solely due to shifts along the \( y \)-axis.
Starting from the partial derivative \( F_x = 3x^2 y z^2 - 4x y z + 3z \), we differentiate with respect to \( y \):
- The term \( 3x^2 y z^2 \) becomes \( 3x^2 z^2 \) after differentiation. Here, \( x^2 z^2 \) is treated as a constant.
- For \( -4x y z \), the partial derivative with respect to \( y \) is \( -4x z \), considering \( 4x z \) constant with respect to \( y \).
- The constant \( 3z \) vanishes in differentiation since it's independent of \( y \).
This step highlights how variations in \( y \) influence the function, holding \( x \) and \( z \) steady. This insight can reveal patterns that arise solely due to shifts along the \( y \)-axis.
Discovering Partial Derivatives with Respect to z
Differentiating with respect to \( z \), we focus on how \( z \) alone affects the function while considering \( x \) and \( y \) as constants. This will complete our understanding of higher-order partial derivatives.
Using \( F_{xy} = 3x^2 z^2 - 4x z \), we differentiate with respect to \( z \):
This derivative helps us understand the impact of changes in \( z \) on the function. By piecing together these partial derivatives, we compile a comprehensive view of how changes in each individual variable alter the entire function.
Using \( F_{xy} = 3x^2 z^2 - 4x z \), we differentiate with respect to \( z \):
- For \( 3x^2 z^2 \), the derivative is \( 6x^2 z \). Here, \( x^2 \) is constant, and the power rule applies to the \( z^2 \) term.
- The term \( -4x z \), once differentiated with respect to \( z \), yields \( -4x \).
This derivative helps us understand the impact of changes in \( z \) on the function. By piecing together these partial derivatives, we compile a comprehensive view of how changes in each individual variable alter the entire function.