Mathematics
Grade 12
15 min
Find values of inverse functions from graphs
Find values of inverse functions from graphs
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1
Introduction & Learning Objectives
Learning Objectives
Define the relationship between a function and its inverse graphically.
Identify the coordinates of a point on the graph of an inverse function, f⁻¹(x), given the graph of the original function, f(x).
Evaluate f⁻¹(a) for a specific value 'a' by interpreting the graph of f(x).
Explain the graphical relationship between the domain and range of a function and its inverse.
Determine if a function has an inverse that is also a function by applying the Horizontal Line Test to its graph.
Solve composite function problems involving inverses, such as f(f⁻¹(b)) or f⁻¹(f(a)), using a graph.
Ever wondered how to 'undo' a function just by looking at its picture? 🖼️ Let's flip our perspective and learn how to read a graph in reverse!
This tuto...
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Key Concepts & Vocabulary
TermDefinitionExample
Inverse Function (f⁻¹(x))A function that 'reverses' or 'undoes' another function. If the original function f takes an input 'a' to an output 'b', the inverse function f⁻¹ takes the input 'b' back to the output 'a'.If f(x) = x³ and we know f(2) = 8, then the inverse function f⁻¹(x) = ³√x gives f⁻¹(8) = 2.
One-to-One FunctionA function where each output value (y) is associated with exactly one input value (x). Only one-to-one functions have inverse functions.f(x) = 2x + 1 is one-to-one. f(x) = x² is not, because f(2) = 4 and f(-2) = 4 (the output 4 comes from two different inputs).
Horizontal Line TestA visual method to determine if a function is one-to-one. If any horizontal line can be drawn that intersects...
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Core Formulas
The Fundamental Inverse Relationship
If f(a) = b, then f⁻¹(b) = a.
This is the core principle for finding inverse values from a graph. To find f⁻¹(b), you are looking for the x-value on the graph of f(x) that produces the y-value of b.
Coordinate Swap Rule
(a, b) on f(x) \iff (b, a) on f⁻¹(x)
This rule translates the algebraic relationship into a graphical one. A point on the original function's graph has its coordinates swapped to become a point on the inverse function's graph.
Composition Cancellation Properties
f(f⁻¹(x)) = x and f⁻¹(f(x)) = x
These rules show that a function and its inverse 'cancel' each other out. This holds for all x in the domain of the inner function. Graphically, this means finding a value, applying f, and then applying...
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Challenging
The graph of a one-to-one function f(x) passes through the points (2, 5) and (6, 2). Solve the equation f⁻¹(x) = 6 for x.
A.5
B.2
C.6
D.Cannot be determined
Challenging
The graph of a one-to-one function f(x) passes through the points (3, 4) and (5, 8). What is the value of f⁻¹(f(3) + 1)?
A.There is not enough information to solve.
B.8
C.3
D.5
Challenging
The graph of a differentiable, one-to-one function f(x) passes through the point (2, 7). The slope of the tangent line to the graph at this point is 3. What is the slope of the tangent line to the graph of f⁻¹(x) at the point (7, 2)?
A.3
B.-3
C.-1/3
D.1/3
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