For the function z = = f(x, y) = x² − xy² + y³, find the equations of the tangent lines in both the x-direction & the y-direction at the point (2, 1, 3).

Calculus: Early Transcendentals
8th Edition
ISBN:9781285741550
Author:James Stewart
Publisher:James Stewart
Chapter1: Functions And Models
Section: Chapter Questions
Problem 1RCC: (a) What is a function? What are its domain and range? (b) What is the graph of a function? (c) How...
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**Topic: Finding Tangent Lines of a Multivariable Function**

**Objective:**
For the function \( z = f(x, y) = x^2 - xy^2 + y^3 \), find the equations of the tangent lines in both the x-direction and the y-direction at the point \( (2, 1, 3) \).

**Function and Point:**
- Function: \( z = f(x, y) = x^2 - xy^2 + y^3 \)
- Point: \( (2, 1, 3) \)

### Step-by-Step Solution:

1. **Find Partial Derivatives:**
   - Partial derivative with respect to \( x \):
     \[
     f_x(x, y) = \frac{\partial}{\partial x} (x^2 - xy^2 + y^3) = 2x - y^2
     \]
   - Partial derivative with respect to \( y \):
     \[
     f_y(x, y) = \frac{\partial}{\partial y} (x^2 - xy^2 + y^3) = -2xy + 3y^2
     \]

2. **Evaluate Partial Derivatives at Point \( (2, 1) \):**
   - \( f_x(2, 1) \):
     \[
     f_x(2, 1) = 2(2) - 1^2 = 4 - 1 = 3
     \]
   - \( f_y(2, 1) \):
     \[
     f_y(2, 1) = -2(2)(1) + 3(1)^2 = -4 + 3 = -1
     \]

3. **Equations of Tangent Lines:**
   - Tangent line in x-direction:
     \[
     z - z_0 = f_x(x_0, y_0)(x - x_0)
     \]
     Given \( (x_0, y_0, z_0) = (2, 1, 3) \), the tangent line equation is:
     \[
     z - 3 = 3(x - 2) \implies z = 3x - 6 + 3 \implies z = 3x - 3
     \]
   -
Transcribed Image Text:**Topic: Finding Tangent Lines of a Multivariable Function** **Objective:** For the function \( z = f(x, y) = x^2 - xy^2 + y^3 \), find the equations of the tangent lines in both the x-direction and the y-direction at the point \( (2, 1, 3) \). **Function and Point:** - Function: \( z = f(x, y) = x^2 - xy^2 + y^3 \) - Point: \( (2, 1, 3) \) ### Step-by-Step Solution: 1. **Find Partial Derivatives:** - Partial derivative with respect to \( x \): \[ f_x(x, y) = \frac{\partial}{\partial x} (x^2 - xy^2 + y^3) = 2x - y^2 \] - Partial derivative with respect to \( y \): \[ f_y(x, y) = \frac{\partial}{\partial y} (x^2 - xy^2 + y^3) = -2xy + 3y^2 \] 2. **Evaluate Partial Derivatives at Point \( (2, 1) \):** - \( f_x(2, 1) \): \[ f_x(2, 1) = 2(2) - 1^2 = 4 - 1 = 3 \] - \( f_y(2, 1) \): \[ f_y(2, 1) = -2(2)(1) + 3(1)^2 = -4 + 3 = -1 \] 3. **Equations of Tangent Lines:** - Tangent line in x-direction: \[ z - z_0 = f_x(x_0, y_0)(x - x_0) \] Given \( (x_0, y_0, z_0) = (2, 1, 3) \), the tangent line equation is: \[ z - 3 = 3(x - 2) \implies z = 3x - 6 + 3 \implies z = 3x - 3 \] -
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