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# 1.15 Connecting Limits at Infinity and Horizontal Asymptotes

Anusha Tekumulla

ethan_bilderbeek

### AP Calculus AB/BCΒ βΎοΈ

279Β resources
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In this section, we will focus on understanding the behavior of functions as they approach infinity in the x-direction. We will explore the concept of limits at infinity and how they relate to horizontal asymptotes in a function.
Objectives:
• Interpret the behavior of functions using limits involving infinity in the x-direction.
• Understand the concept of limits at infinity.
• Describe and explain asymptotic and unbounded behavior of functions using limits.
Essential Knowledge:
• The concept of a limit can be extended to include limits at infinity in the x-direction.
• Asymptotic and unbounded behavior of functions in the x-direction can be described and explained using limits at infinity.
When a function approaches a value of positive or negative infinity in the x-direction, the limit is said to be infinite. For example, if a function f(x) approaches positive infinity as x approaches positive infinity, we would write the limit as:
lim x->+infinity f(x) = +infinity
Similarly, if a function approaches negative infinity as x approaches negative infinity, we would write the limit as:
lim x->-infinity f(x) = -infinity
In both cases, the limit does not exist in the traditional sense, as the function does not approach a specific value. Instead, the limit tells us about the behavior of the function as x approaches infinity.
Horizontal asymptotes are another way to describe the behavior of a function as it approaches infinity in the x-direction. A horizontal asymptote occurs when the function approaches a constant value as x approaches positive or negative infinity.
For example, a function with a horizontal asymptote at y = a would be written as:
f(x) = a + 1/x
As x approaches positive or negative infinity, the denominator (1/x) becomes smaller and smaller, causing the value of the function to approach the constant value of a. This results in a horizontal asymptote at y = a.
Let's look at some examples to further illustrate the concept of limits at infinity and horizontal asymptotes:
1. f(x) = x, as x approaches positive infinity, the function approaches positive infinity, and we would write the limit as: lim x->+infinity f(x) = +infinity This function has no horizontal asymptote
2. g(x) = x^2, as x approaches positive infinity, the function approaches positive infinity, and we would write the limit as: lim x->+infinity g(x) = +infinity This function has no horizontal asymptote
3. h(x) = x^2-2x-3, as x approaches positive and negative infinity, the function approaches positive and negative infinity respectively, and we would write the limit as: lim x->+infinity h(x) = +infinity, lim x->-infinity h(x) = -infinity This function has no horizontal asymptote
4. j(x) = x^3+3x^2+3x+1/(x+1), as x approaches positive infinity, the function approaches 1, and we would write the limit as: lim x->+infinity j(x) = 1 As x moves closerto positive infinity, the denominator (x+1) becomes larger and larger, causing the value of the function to approach the constant value of 1. This results in a horizontal asymptote at y = 1.
5. k(x) = 1/x, as x approaches positive infinity, the function approaches 0, and we would write the limit as: lim x->+infinity k(x) = 0 As x moves closer to positive infinity, the denominator becomes larger and larger, causing the value of the function to approach 0. This results in a horizontal asymptote at y = 0.
6. l(x) = 1/x^2, as x approaches positive infinity, the function approaches 0, and we would write the limit as: lim x->+infinity l(x) = 0 As x moves closer to positive infinity, the denominator becomes larger and larger, causing the value of the function to approach 0. This results in a horizontal asymptote at y = 0.
7. m(x) = x^2+x-6/x+2, as x approaches positive infinity and -2, the function approaches 1 and -3 respectively, and we would write the limit as: lim x->+infinity m(x) = 1, lim x->-2 m(x) = -3 As x moves closer to positive infinity and -2, the denominator becomes larger and larger, causing the value of the function to approach 1 and -3 respectively. This results in horizontal asymptotes at y = 1 and y = -3.
8. n(x) = x^2-5x+6/x^2-4x+4, as x approaches positive and negative infinity, the function approaches 1 and -1 respectively, and we would write the limit as: lim x->+infinity n(x) = 1, lim x->-infinity n(x) = -1 As x moves closer to positive and negative infinity, the denominator becomes larger and larger, causing the value of the function to approach 1 and -1 respectively. This results in horizontal asymptotes at y = 1 and y = -1.
9. p(x) = x^3-9x+3/x^2+1, as x approaches positive and negative infinity, the function approaches 0, and we would write the limit as: lim x->+infinity p(x) = 0, lim x->-infinity p(x) = 0 As x moves closer to positive and negative infinity, the denominator becomes larger and larger, causing the value of the function to approach 0. This results in horizontal asymptote at y = 0.
10. q(x) = (x^2-4)/(x^2-16), as x approaches positive and negative infinity, the function approaches 0, and we would write the limit as: lim x->+infinity q(x) = 0, lim x->-infinity q(x) = 0 As x moves closer to positive and negative infinity, the denominator becomes larger and larger, causing the value of the function to approach 0. This results in a horizontal asymptote at y = 0.
In summary, understanding limits at infinity and horizontal asymptotes is crucial for interpreting the behavior of functions as they approach infinity in the x-direction. By using limits and analyzing the behavior of functions, we can gain a better understanding of the asymptotic
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