Mathematics
Grade 12
15 min
Find limits of polynomials and rational functions
Find limits of polynomials and rational functions
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1
Introduction & Learning Objectives
Learning Objectives
Evaluate the limit of any polynomial function using direct substitution.
Evaluate the limit of a rational function at a point where the denominator is non-zero.
Identify the indeterminate form 0/0 when evaluating limits of rational functions.
Apply algebraic techniques, such as factoring and cancelling, to resolve the indeterminate form 0/0.
Determine the limit of a rational function as x approaches positive or negative infinity by analyzing the degrees of the numerator and denominator.
Distinguish between limits that approach a finite number, infinity, negative infinity, or do not exist.
What happens to the value of a function as you get infinitely close to a specific point, without ever actually touching it? 🤔
This tutorial will equip you with the fun...
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Key Concepts & Vocabulary
TermDefinitionExample
LimitThe value that a function f(x) approaches as the input x approaches some value c. We write this as lim_{x->c} f(x) = L.For the function f(x) = x + 2, as x gets closer to 3, f(x) gets closer to 5. So, lim_{x->3} (x + 2) = 5.
Polynomial FunctionA function consisting of variables and coefficients, involving only the operations of addition, subtraction, multiplication, and non-negative integer exponents of variables.P(x) = 4x^3 - 2x^2 + x - 10
Rational FunctionA function that can be expressed as the ratio of two polynomial functions, R(x) = P(x) / Q(x), where the denominator Q(x) is not the zero polynomial.R(x) = (x^2 - 4) / (x + 1)
Direct SubstitutionThe primary method for finding limits of well-behaved functions (like polynomials) by simply plugging the valu...
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Core Formulas
Limit of a Polynomial Function
If P(x) is a polynomial function and c is any real number, then: lim_{x->c} P(x) = P(c)
To find the limit of any polynomial at any point, always use direct substitution. Polynomials are continuous everywhere, so the limit is always the function's value at that point.
Limit of a Rational Function
If R(x) = P(x)/Q(x) is a rational function and c is a real number such that Q(c) ≠0, then: lim_{x->c} R(x) = P(c) / Q(c)
Use direct substitution for rational functions as long as the denominator does not become zero. If the denominator is zero, you must use other techniques.
Limits of Rational Functions at Infinity
For R(x) = (a_n x^n + ...)/(b_m x^m), the limit as x->±∞ is determined by the degrees n and m:
1. If n < m, the lim...
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Challenging
Find the value of the constant 'a' such that the limit exists: lim_{x->1} (x^2 + ax - 5) / (x - 1)
A.4
B.-5
C.1
D.-4
Challenging
Evaluate the limit: lim_{x->2} (x^3 - 2x^2 - 4x + 8) / (x^2 - 4)
A.4
B.0
C.1
D.Does Not Exist
Challenging
Evaluate the limit: lim_{x->-∞} (4x - 3x^3) / (x^2 + 2x + 5)
A.-3
B.-∞
C.∞
D.0
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