Math Problem Statement

Evaluate the limit: lim (x, y) → (0, 0) (x^3y - 2y) / (x^2 + xy + y^2)

Solution

The given limit problem is:

lim(x,y)(0,0)x3y2yx2+xy+y2\lim_{(x, y) \to (0, 0)} \frac{x^3 y - 2y}{x^2 + xy + y^2}

Step 1: Analyzing the Limit

We need to evaluate the limit as (x,y)(x, y) approaches (0,0)(0, 0). This is a multivariable limit, so the approach to zero can vary based on the path we choose. To verify whether the limit exists, we can evaluate the limit along different paths.

Step 2: Path 1: Along y=0y = 0

When y=0y = 0, the expression becomes:

x3(0)2(0)x2+x(0)+(0)2=0x2=0\frac{x^3(0) - 2(0)}{x^2 + x(0) + (0)^2} = \frac{0}{x^2} = 0

So, along y=0y = 0, the limit is 0.

Step 3: Path 2: Along x=0x = 0

When x=0x = 0, the expression becomes:

03(y)2y02+0(y)+y2=2yy2=2y\frac{0^3(y) - 2y}{0^2 + 0(y) + y^2} = \frac{-2y}{y^2} = \frac{-2}{y}

As y0y \to 0, 2y\frac{-2}{y} does not approach a finite value; instead, it goes to infinity or negative infinity depending on the direction from which yy approaches 0. Therefore, the limit does not exist along this path.

Conclusion:

Since the limit behaves differently along different paths, the overall limit does not exist.

Would you like more details or have any questions about the steps?


Here are 5 related questions to further your understanding:

  1. How do you determine if a multivariable limit exists?
  2. Why is evaluating limits along different paths important for multivariable limits?
  3. What does it mean if a limit approaches different values along different paths?
  4. Can the polar coordinate substitution method help for other multivariable limit problems?
  5. What is the definition of continuity for a function of multiple variables?

Tip: When dealing with multivariable limits, always try evaluating the function along different paths to check if the limit is path-dependent.

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Math Problem Analysis

Mathematical Concepts

Multivariable Calculus
Limits
Path-Dependence

Formulas

lim (x, y) → (0, 0) f(x, y)

Theorems

Multivariable Limits Theorem
Path Independence Theorem

Suitable Grade Level

Undergraduate - Calculus