AP Calculus AB/BC: Connecting Infinite Limits and Vertical Asymptotes Study Guide
Introduction
Greetings, mathletes! Ready to dive deep into the world of infinite limits and vertical asymptotes? Grab your graphing calculator and your sense of humor, because we’re about to make calculus as fun as watching cat videos on the internet! 😸🔢
Discontinuities: The Party Poopers of Functions
Discontinuities are like speed bumps in the smooth road of a function. They are those pesky points where a function suddenly decides to misbehave, like your WiFi cutting out during a crucial moment in a streaming marathon. In calculus, many powerful theorems need smooth, continuous functions, so we must become experts at spotting discontinuities. And today, our main focus is on one specific kind: vertical asymptotes.
Vertical Asymptotes: The Brick Walls of the Graph World
Remember from Algebra II when vertical asymptotes were those invisible barriers a function would flirt with but never cross? If a function were a car, vertical asymptotes would be those “Do Not Enter” signs that every decent function obeys. 🚧
Vertical asymptotes are a type of discontinuity where the function's yvalue rockets off to infinity as it gets close to a specific xvalue. It’s like the function is auditioning for "America’s Got Infinite Talent" by showing off how quickly it can grow without bounds. Mathematically speaking, these occur when the function approaches some value but, instead of reaching it, the function’s values go on an infinite rollercoaster ride.
Imagine our beloved function ( f(x) = \frac{1}{x} ). At ( x = 0 ), the function hits a vertical asymptote, because trying to divide by zero is like trying to eat soup with a fork—impossible and messy. 🤯
Infinite Limits: To Infinity and Beyond! ♾️
An infinite limit occurs when a function’s values grow beyond all bounds (either positive or negative) as the input approaches a certain value. It’s like our function is heading off on an endless road trip without ever running out of gas. 🚗💨
To connect infinite limits with vertical asymptotes, we use limits of the form:
 ( \lim_{{x \to a}} f(x) = \pm \infty )
 ( \lim_{{x \to a^+}} f(x) = \pm \infty )
 ( \lim_{{x \to a^}} f(x) = \pm \infty )
Connecting Infinite Limits to Vertical Asymptotes
When you see these scenarios, it's a red flag that a vertical asymptote exists at ( x = a ). The function can approach infinity from the left (()), the right ((+)), or both sides. Just don't expect your function's yvalue to ever play it cool as it nears this xvalue. It’s partying all the way to infinity.
Example Time: Let's Prove Those Asymptotes!
Example 1: Proving ( x = 3 ) is a Vertical Asymptote for ( f(x) = \frac{1}{x+3} )
To show ( x = 3 ) is a vertical asymptote, we check the limit as ( x ) approaches (3).

From the right (( x \to 3^+ )): [ \lim_{{x \to 3^+}} \frac{1}{x+3} = \infty ] As ( x ) gets close to (3) from the right (think (2.99999)), the denominator approaches 0, making the fraction’s value skyrocket to positive infinity. 🌠

From the left (( x \to 3^ )): [ \lim_{{x \to 3^}} \frac{1}{x+3} = \infty ] Here, as ( x ) gets close to (3) from the left (think (3.00001)), the denominator approaches 0, but will cause the fraction’s value to nosedive to negative infinity. 🌌
Conclusion: The infinite limits confirm that ( x = 3 ) is indeed a vertical asymptote.
Example 2: Finding the Vertical Asymptote for ( f(x) = \ln(x) )
Good ol’ natural logarithm! The graph of ( \ln(x) ) has a steep dropoff as it approaches ( x = 0 ).
[ \lim_{{x \to 0^+}} \ln(x) = \infty ]
As ( x ) shrinks closer to 0 from the positive side, ( \ln(x) ) dives down infinitely. ( x = 0 ) is the vertical asymptote for this function. Think of it as the Bermuda Triangle for logarithms; no value survives the journey to zero.
Key Concepts to Remember
 Continuity: Whether a function has breaks, holes, or jumps. Think of it as a movie with no commercial breaks.
 Vertical Asymptote: A line ( x = a ) that the function will forever approach but never cross.
 Infinite Limit: What the function's output does as the input heads off toward a specific value, leading to either positive or negative infinity.
 Horizontal Asymptote: The yvalue that a graph approaches as ( x ) goes towards positive or negative infinity. Like a function's chillout zone.
Fun Fact
Did you know "asymptote" comes from a Greek word meaning "not falling together"? So, asymptotes are like friends who promise to hang out but never really do. 😅
Conclusion
Ready to conquer those infinite limits and vertical asymptotes? You’ve got this! Remember, if your function starts behaving like it's on a sugar rush, check for discontinuities or vertical asymptotes. Happy calculusing! 🧮✨
Go forth and limit your fears of limits, and may the (calculus) force be with you!