The behavior of a function near the limit point is crucial in determining the limit itself because the limit essentially describes what the function values are approaching as the input approaches a certain point. Here’s how it works:

1. Continuity at the Limit Point:

• If the function is continuous at the limit point $x = c$, the limit is simply the value of the function at that point: $\lim_{x \to c} f(x) = f(c)$
• In this case, the behavior of the function near $x = c$ is predictable and smooth, with no sudden jumps or undefined points.

2. Discontinuity at the Limit Point:

• If the function is not continuous at $x = c$, the limit can still exist, but it depends on how the function behaves as $x$ approaches $c$ from both sides (left and right). The limit exists if the function values from both sides approach the same number.
• Example: Consider the function $f(x) = \frac{|x|}{x}$ near $x = 0$. The limit as $x$ approaches 0 does not exist because the function behaves differently on either side of 0: $\lim_{x \to 0^-} f(x) = -1 \quad \text{and} \quad \lim_{x \to 0^+} f(x) = 1$

3. Approaching an Indeterminate Form:

• Sometimes, as $x$ approaches the limit point, the function may lead to an indeterminate form, such as $\frac{0}{0}$ or $\frac{\infty}{\infty}$. This often happens if both the numerator and denominator approach zero.
• In these cases, the behavior of the function near the limit point might be complex, and techniques like factorization, L'Hôpital's rule, or algebraic manipulation are needed to resolve the indeterminate form and find the limit.

4. Asymptotic Behavior:

• If a function has an asymptote near the limit point, the function values may approach infinity or negative infinity. For example: \quad \text{and} \quad \lim_{x \to 0^-} \frac{1}{x} = -\infty$$
• In this case, the function’s behavior indicates that as $x$ gets closer to 0, the function grows without bound.

5. Oscillatory Behavior:

• Some functions might oscillate near the limit point, making it difficult or impossible to define a limit. For instance, $\lim_{x \to 0} \sin\left(\frac{1}{x}\right)$ does not exist because the function oscillates infinitely as $x$ approaches 0.

Summary

The key takeaway is that the limit depends not just on the value of the function at the limit point but on how the function behaves as it gets very close to that point. Understanding this behavior allows us to determine whether the limit exists and, if so, what the limit is.

Would you like more detailed examples on any specific type of behavior? Here are some related questions:

1. How does L'Hôpital's rule help when dealing with indeterminate forms like $\frac{0}{0}$?
2. What is a removable discontinuity, and how does it affect the limit of a function?
3. How can you use one-sided limits to analyze the behavior of functions near points of discontinuity?
4. Can a limit exist at a point where the function itself is undefined? How?
5. What are some common functions that exhibit oscillatory behavior near certain points?

Tip: Always analyze the function's behavior from both sides of the limit point, especially if the function has potential discontinuities or undefined points. This helps in accurately determining whether the limit exists and what its value might be.