Math Problem Statement

Determine the gradient of f(x, y) = e^(2x) sin(3y) at (x, y) = (2, -2).

Solution

To find the gradient of the function f(x,y)=e2xsin(3y)f(x, y) = e^{2x} \sin(3y) at the point (x,y)=(2,2)(x, y) = (2, -2), we need to compute the partial derivatives of f(x,y)f(x, y) with respect to both xx and yy, and then evaluate those partial derivatives at the given point.

Step 1: Compute fx\frac{\partial f}{\partial x}

We treat yy as a constant and differentiate f(x,y)=e2xsin(3y)f(x, y) = e^{2x} \sin(3y) with respect to xx: fx=ddx(e2xsin(3y))\frac{\partial f}{\partial x} = \frac{d}{dx} \left( e^{2x} \sin(3y) \right) Using the chain rule for e2xe^{2x}, we get: fx=2e2xsin(3y)\frac{\partial f}{\partial x} = 2e^{2x} \sin(3y)

Step 2: Compute fy\frac{\partial f}{\partial y}

Now we treat xx as a constant and differentiate f(x,y)=e2xsin(3y)f(x, y) = e^{2x} \sin(3y) with respect to yy: fy=ddy(e2xsin(3y))\frac{\partial f}{\partial y} = \frac{d}{dy} \left( e^{2x} \sin(3y) \right) Using the chain rule for sin(3y)\sin(3y), we get: fy=3e2xcos(3y)\frac{\partial f}{\partial y} = 3e^{2x} \cos(3y)

Step 3: Evaluate the partial derivatives at (x,y)=(2,2)(x, y) = (2, -2)

Evaluate fx\frac{\partial f}{\partial x} at (2,2)(2, -2):

fx(2,2)=2e2(2)sin(3(2))=2e4sin(6)\frac{\partial f}{\partial x} (2, -2) = 2e^{2(2)} \sin(3(-2)) = 2e^4 \sin(-6) Using e454.5982e^4 \approx 54.5982 and sin(6)0.2794\sin(-6) \approx 0.2794: fx(2,2)=2×54.5982×(0.2794)30.5071\frac{\partial f}{\partial x} (2, -2) = 2 \times 54.5982 \times (-0.2794) \approx -30.5071

Evaluate fy\frac{\partial f}{\partial y} at (2,2)(2, -2):

fy(2,2)=3e2(2)cos(3(2))=3e4cos(6)\frac{\partial f}{\partial y} (2, -2) = 3e^{2(2)} \cos(3(-2)) = 3e^4 \cos(-6) Using cos(6)0.9602\cos(-6) \approx 0.9602: fy(2,2)=3×54.5982×0.9602157.2321\frac{\partial f}{\partial y} (2, -2) = 3 \times 54.5982 \times 0.9602 \approx 157.2321

Step 4: Write the gradient

The gradient f(2,2)\nabla f(2, -2) is given by the vector: f(2,2)=(fx(2,2),fy(2,2))\nabla f(2, -2) = \left( \frac{\partial f}{\partial x} (2, -2), \frac{\partial f}{\partial y} (2, -2) \right) Thus, f(2,2)(30.5071,157.2321)\nabla f(2, -2) \approx (-30.5071, 157.2321)

Let me know if you'd like more details or have any questions!


Here are some related questions:

  1. How is the chain rule applied in calculating gradients?
  2. Why is the cosine function used in the derivative with respect to yy?
  3. How does the exponential term affect the gradient's magnitude?
  4. What is the geometric interpretation of the gradient vector?
  5. How would the gradient change if we modified the function slightly, such as by changing the coefficients in the sine or exponential terms?

Tip: Always double-check your trigonometric and exponential values for accuracy when dealing with gradients that require evaluating specific points.

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Math Problem Analysis

Mathematical Concepts

Calculus
Partial Derivatives
Multivariable Functions
Gradients

Formulas

Gradient of f(x, y): ∇f(x, y) = (∂f/∂x, ∂f/∂y)
Partial derivative of e^(2x) sin(3y) with respect to x: ∂f/∂x = 2e^(2x) sin(3y)
Partial derivative of e^(2x) sin(3y) with respect to y: ∂f/∂y = 3e^(2x) cos(3y)

Theorems

Chain Rule
Product Rule in Partial Differentiation

Suitable Grade Level

Undergraduate Calculus