Mathematics Grade 9 15 min

Domain and range of exponential functions

Domain and range of exponential functions

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Introduction & Learning Objectives

Learning Objectives Define domain and range in the context of exponential functions. Identify the domain of any exponential function of the form f(x) = a * b^(x-h) + k. Identify the horizontal asymptote of a transformed exponential function. Determine the range of a transformed exponential function by analyzing its vertical shift (k) and reflection (a). Express the domain and range of exponential functions using both interval notation and set-builder notation. Explain how transformations, specifically vertical shifts, affect the range of an exponential function. Ever wonder how a single social media post can go viral, reaching millions of people in just a few hours? 📈 That's the power of exponential growth! In this tutorial, we'll explore the 'inputs' (...
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Key Concepts & Vocabulary

TermDefinitionExample Exponential FunctionA function where the variable is in the exponent, typically in the form f(x) = b^x, where the base 'b' is a positive constant other than 1.f(x) = 2^x is an exponential growth function. g(x) = (1/2)^x is an exponential decay function. DomainThe complete set of all possible input values (x-values) for which the function is defined.For the function f(x) = 3^x, you can plug in any real number for x (like -2, 0, 5.5), so the domain is all real numbers. RangeThe complete set of all possible output values (y-values) that a function can produce.For f(x) = 3^x, the output y is always a positive number (e.g., 3^-2 = 1/9, 3^0 = 1, 3^2 = 9). The range is all positive real numbers, y > 0. Horizontal AsymptoteA horizontal line that the graph of a f...
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Core Formulas

Domain of an Exponential Function For any exponential function f(x) = a * b^(x-h) + k, the domain is always the set of all real numbers. This is because you can substitute any real number for x in the exponent. There are no restrictions like division by zero or square roots of negative numbers. In set-builder notation: {x | x ∈ ℝ}. In interval notation: (-∞, ∞). Range of an Exponential Function For f(x) = a * b^(x-h) + k, the horizontal asymptote is y = k. The range depends on the sign of 'a'. If 'a' is positive (a > 0), the graph opens upward from the asymptote, so the range is y > k. If 'a' is negative (a < 0), the graph is reflected and opens downward from the asymptote, so the range is y < k.

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Sample Practice Questions

Challenging
If two exponential functions, f(x) = a₁b₁^(x-h₁) + k₁ and g(x) = a₂b₂^(x-h₂) + k₂, have the exact same range, what must be true about their parameters?
A.a₁ = a₂ and k₁ = k₂
B.k₁ = k₂ and the signs of a₁ and a₂ are the same.
C.b₁ = b₂ and h₁ = h₂
D.The signs of a₁ and a₂ are opposite.
Challenging
An exponential function f(x) has a range of (k, ∞). If a new function is defined as g(x) = -f(x), what is the range of g(x)?
A.(-∞, -k)
B.(-k, ∞)
C.(-∞, k)
D.(k, ∞)
Challenging
An exponential function has a domain of {x | x ∈ ℝ} and a range of {y | y > -4}. Which of the following functions is IMPOSSIBLE given these conditions?
A.f(x) = 2^x - 4
B.f(x) = 3 * (1/2)^(x+1) - 4
C.f(x) = -1 * 5^x - 4
D.f(x) = 0.1 * 10^x - 4

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