Mathematics
Grade 12
15 min
Find values of functions from graphs
Find values of functions from graphs
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1
Introduction & Learning Objectives
Learning Objectives
Find the value of a function, f(x), for a specific input, x, by reading its graph.
Find the input value(s), x, for a given function output, f(x).
Evaluate arithmetic combinations of functions, such as (f+g)(x) or (f/g)(x), using their graphs.
Evaluate composite functions, such as f(g(x)), by sequentially reading values from graphs.
Determine the value of a limit (lim x→c f(x)) from a graph, distinguishing it from the function's value at that point, f(c).
Approximate the value of a definite integral (∫[a,b] f(x) dx) by interpreting it as the net signed area under the curve.
Ever seen a heart monitor in a hospital? 🩺 Doctors read those graphs instantly to understand a patient's condition—they're finding function values in real-time!
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Key Concepts & Vocabulary
TermDefinitionExample
Function Value at a PointThe output of a function for a given input. On a graph, for an input 'c' on the x-axis, the function value f(c) is the corresponding y-coordinate of the point on the curve.If the point (3, 5) is on the graph of f(x), then f(3) = 5.
Point of DiscontinuityA point on the graph where the function is not continuous. This can be a 'hole' (a single missing point, also called a removable discontinuity) or a 'jump' (where the graph breaks and continues at a different y-value).A graph might have an open circle at (2, 4), indicating f(2) is undefined, even though the graph approaches a y-value of 4 from both sides.
Limit of a Function from a GraphThe y-value that a function's graph approaches as the x-value gets closer...
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Core Formulas
Evaluating a Function
y = f(c)
To find the value of a function f(x) at x=c, locate 'c' on the horizontal axis (x-axis). Move vertically until you intersect the graph of the function. Then, move horizontally to find the corresponding value on the vertical axis (y-axis). This y-value is f(c).
Arithmetic Combinations of Functions
(f \pm g)(c) = f(c) \pm g(c) \quad and \quad (f/g)(c) = f(c) / g(c), g(c) \neq 0
To find the value of a combination of functions at x=c, first find the individual values of f(c) and g(c) from their respective graphs. Then, perform the specified arithmetic operation (addition, subtraction, multiplication, or division).
Composition of Functions
(f \circ g)(c) = f(g(c))
To evaluate a composite function, work from the inside out. First, f...
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Sign Up Free to ContinueSample Practice Questions
Challenging
The graph of h(x) consists of a quarter-circle of radius 2 in the first quadrant (from (2,0) to (0,2)) and a line segment from (0,2) to (-2,0). What is the average value of h(x) on the interval [-2, 2]?
A.(π + 2) / 2
B.(π + 2) / 4
C.π + 2
D.π
Challenging
The graph of f(x) is a semicircle of radius 2 centered at the origin. The graph of g(x) has a hole at (0, 3) and a solid dot at (0, 1). Find the value of f(g(0) + lim x→0 g(x)).
A.0
B.1
C.2
D.Undefined
Easy
The following questions refer to the graphs of f(x), g(x), and h(x).
- f(x): A line from (-4, 4) to (-1, 1), then the parabola y=x² from x=-1 to x=1, then a line from (1, 1) to (4, -2). There is a hole at (1, 1) and a solid point at (1, 3).
- g(x): A line from (-4, -2) to (0, 2), then the bottom half of a circle with radius 2 centered at (2, 2) for x in [0, 4]. There is a hole at (0, 2) and a solid point at (0, -1).
- h(x): Line segments connecting (-4, -1), (-2, 3), (0, 1), (2, 1), and (4, 4).
Using the graph of h(x), find the value of h(-2).
A.1
B.3
C.-1
D.0
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