1. Section 2.2
A Catalogue of Essential Functions
V63.0121.021/041, Calculus I
New York University
September 8, 2010
Announcements
First WebAssign-ments are due September 13
First written assignment is due September 15
Do the Get-to-Know-You survey for extra credit!
. . . . . .
2. Announcements
First WebAssign-ments are
due September 13
First written assignment is
due September 15
Do the Get-to-Know-You
survey for extra credit!
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 2 / 31
3. Objectives: A Catalog of Essential Functions
Identify different classes of
algebraic functions,
including polynomial
(linear, quadratic, cubic,
etc.), polynomial
(especially linear,
quadratic, and cubic),
rational, power,
trigonometric, and
exponential functions.
Understand the effect of
algebraic transformations
on the graph of a function.
Understand and compute
the composition of two
functions. . . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 3 / 31
4. What is a function?
Definition
A function f is a relation which assigns to to every element x in a set D
a single element f(x) in a set E.
The set D is called the domain of f.
The set E is called the target of f.
The set { y | y = f(x) for some x } is called the range of f.
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 4 / 31
5. Classes of Functions
linear functions, defined by slope an intercept, point and point, or
point and slope.
quadratic functions, cubic functions, power functions, polynomials
rational functions
trigonometric functions
exponential/logarithmic functions
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 5 / 31
6. Outline
Linear functions
Other Polynomial functions
Other power functions
Rational functions
Trigonometric Functions
Exponential and Logarithmic functions
Transformations of Functions
Compositions of Functions
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 6 / 31
7. Linear functions
Linear functions have a constant rate of growth and are of the form
f(x) = mx + b.
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 7 / 31
8. Linear functions
Linear functions have a constant rate of growth and are of the form
f(x) = mx + b.
Example
In New York City taxis cost $2.50 to get in and $0.40 per 1/5 mile. Write
the fare f(x) as a function of distance x traveled.
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 7 / 31
9. Linear functions
Linear functions have a constant rate of growth and are of the form
f(x) = mx + b.
Example
In New York City taxis cost $2.50 to get in and $0.40 per 1/5 mile. Write
the fare f(x) as a function of distance x traveled.
Answer
If x is in miles and f(x) in dollars,
f(x) = 2.5 + 2x
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 7 / 31
10. Example
Biologists have noticed that the chirping rate of crickets of a certain
species is related to temperature, and the relationship appears to be
very nearly linear. A cricket produces 113 chirps per minute at 70 ◦ F
and 173 chirps per minute at 80 ◦ F.
(a) Write a linear equation that models the temperature T as a function
of the number of chirps per minute N.
(b) What is the slope of the graph? What does it represent?
(c) If the crickets are chirping at 150 chirps per minute, estimate the
temperature.
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 8 / 31
12. Solution
The point-slope form of the equation for a line is appropriate
here: If a line passes through (x0 , y0 ) with slope m, then the line
has equation
y − y0 = m(x − x0 )
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 9 / 31
13. Solution
The point-slope form of the equation for a line is appropriate
here: If a line passes through (x0 , y0 ) with slope m, then the line
has equation
y − y0 = m(x − x0 )
80 − 70 10 1
The slope of our line is = =
173 − 113 60 6
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 9 / 31
14. Solution
The point-slope form of the equation for a line is appropriate
here: If a line passes through (x0 , y0 ) with slope m, then the line
has equation
y − y0 = m(x − x0 )
80 − 70 10 1
The slope of our line is = =
173 − 113 60 6
So an equation for T and N is
1 1 113
T − 70 = (N − 113) =⇒ T = N − + 70
6 6 6
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 9 / 31
15. Solution
The point-slope form of the equation for a line is appropriate
here: If a line passes through (x0 , y0 ) with slope m, then the line
has equation
y − y0 = m(x − x0 )
80 − 70 10 1
The slope of our line is = =
173 − 113 60 6
So an equation for T and N is
1 1 113
T − 70 = (N − 113) =⇒ T = N − + 70
6 6 6
37
If N = 150, then T = + 70 = 76 1 ◦ F
6
6
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 9 / 31
16. Outline
Linear functions
Other Polynomial functions
Other power functions
Rational functions
Trigonometric Functions
Exponential and Logarithmic functions
Transformations of Functions
Compositions of Functions
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 10 / 31
17. Quadratic functions take the form
f(x) = ax2 + bx + c
The graph is a parabola which opens upward if a > 0, downward if
a < 0.
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 11 / 31
18. Quadratic functions take the form
f(x) = ax2 + bx + c
The graph is a parabola which opens upward if a > 0, downward if
a < 0.
Cubic functions take the form
f(x) = ax3 + bx2 + cx + d
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 11 / 31
19. Example
A parabola passes through (0, 3), (3, 0), and (2, −1). What is the
equation of the parabola?
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 12 / 31
20. Example
A parabola passes through (0, 3), (3, 0), and (2, −1). What is the
equation of the parabola?
Solution
The general equation is y = ax2 + bx + c.
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 12 / 31
21. Example
A parabola passes through (0, 3), (3, 0), and (2, −1). What is the
equation of the parabola?
Solution
The general equation is y = ax2 + bx + c. Each point gives an
equation relating a, b, and c:
3 = a · 02 + b · 0 + c
−1 = a · 22 + b · 2 + c
0 = a · 32 + b · 3 + c
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 12 / 31
22. Example
A parabola passes through (0, 3), (3, 0), and (2, −1). What is the
equation of the parabola?
Solution
The general equation is y = ax2 + bx + c. Each point gives an
equation relating a, b, and c:
3 = a · 02 + b · 0 + c
−1 = a · 22 + b · 2 + c
0 = a · 32 + b · 3 + c
Right away we see c = 3. The other two equations become
−4 = 4a + 2b
−3 = 9a + 3b
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 12 / 31
23. Solution (Continued)
Multiplying the first equation by 3 and the second by 2 gives
−12 = 12a + 6b
−6 = 18a + 6b
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 13 / 31
24. Solution (Continued)
Multiplying the first equation by 3 and the second by 2 gives
−12 = 12a + 6b
−6 = 18a + 6b
Subtract these two and we have −6 = −6a =⇒ a = 1.
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 13 / 31
25. Solution (Continued)
Multiplying the first equation by 3 and the second by 2 gives
−12 = 12a + 6b
−6 = 18a + 6b
Subtract these two and we have −6 = −6a =⇒ a = 1. Substitute
a = 1 into the first equation and we have
−12 = 12 + 6b =⇒ b = −4
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 13 / 31
26. Solution (Continued)
Multiplying the first equation by 3 and the second by 2 gives
−12 = 12a + 6b
−6 = 18a + 6b
Subtract these two and we have −6 = −6a =⇒ a = 1. Substitute
a = 1 into the first equation and we have
−12 = 12 + 6b =⇒ b = −4
So our equation is
y = x2 − 4x + 3
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 13 / 31
27. Outline
Linear functions
Other Polynomial functions
Other power functions
Rational functions
Trigonometric Functions
Exponential and Logarithmic functions
Transformations of Functions
Compositions of Functions
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 14 / 31
28. Whole number powers: f(x) = xn .
1
negative powers are reciprocals: x−3 = 3 .
x
√
fractional powers are roots: x1/3 = 3 x.
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 15 / 31
29. Outline
Linear functions
Other Polynomial functions
Other power functions
Rational functions
Trigonometric Functions
Exponential and Logarithmic functions
Transformations of Functions
Compositions of Functions
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 16 / 31
30. Definition
A rational function is a quotient of polynomials.
Example
x3 (x + 3)
The function f(x) = is rational.
(x + 2)(x − 1)
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 17 / 31
31. Outline
Linear functions
Other Polynomial functions
Other power functions
Rational functions
Trigonometric Functions
Exponential and Logarithmic functions
Transformations of Functions
Compositions of Functions
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 18 / 31
32. Sine and cosine
Tangent and cotangent
Secant and cosecant
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 19 / 31
33. Outline
Linear functions
Other Polynomial functions
Other power functions
Rational functions
Trigonometric Functions
Exponential and Logarithmic functions
Transformations of Functions
Compositions of Functions
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 20 / 31
34. exponential functions (for example f(x) = 2x )
logarithmic functions are their inverses (for example f(x) = log2 (x))
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 21 / 31
35. Outline
Linear functions
Other Polynomial functions
Other power functions
Rational functions
Trigonometric Functions
Exponential and Logarithmic functions
Transformations of Functions
Compositions of Functions
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 22 / 31
36. Transformations of Functions
Take the squaring function and graph these transformations:
y = (x + 1)2
y = (x − 1)2
y = x2 + 1
y = x2 − 1
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 23 / 31
37. Transformations of Functions
Take the squaring function and graph these transformations:
y = (x + 1)2
y = (x − 1)2
y = x2 + 1
y = x2 − 1
Observe that if the fiddling occurs within the function, a transformation
is applied on the x-axis. After the function, to the y-axis.
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 23 / 31
38. Vertical and Horizontal Shifts
Suppose c > 0. To obtain the graph of
y = f(x) + c, shift the graph of y = f(x) a distance c units
y = f(x) − c, shift the graph of y = f(x) a distance c units
y = f(x − c), shift the graph of y = f(x) a distance c units
y = f(x + c), shift the graph of y = f(x) a distance c units
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 24 / 31
39. Vertical and Horizontal Shifts
Suppose c > 0. To obtain the graph of
y = f(x) + c, shift the graph of y = f(x) a distance c units upward
y = f(x) − c, shift the graph of y = f(x) a distance c units
y = f(x − c), shift the graph of y = f(x) a distance c units
y = f(x + c), shift the graph of y = f(x) a distance c units
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 24 / 31
40. Vertical and Horizontal Shifts
Suppose c > 0. To obtain the graph of
y = f(x) + c, shift the graph of y = f(x) a distance c units upward
y = f(x) − c, shift the graph of y = f(x) a distance c units downward
y = f(x − c), shift the graph of y = f(x) a distance c units
y = f(x + c), shift the graph of y = f(x) a distance c units
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 24 / 31
41. Vertical and Horizontal Shifts
Suppose c > 0. To obtain the graph of
y = f(x) + c, shift the graph of y = f(x) a distance c units upward
y = f(x) − c, shift the graph of y = f(x) a distance c units downward
y = f(x − c), shift the graph of y = f(x) a distance c units to the right
y = f(x + c), shift the graph of y = f(x) a distance c units
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 24 / 31
42. Vertical and Horizontal Shifts
Suppose c > 0. To obtain the graph of
y = f(x) + c, shift the graph of y = f(x) a distance c units upward
y = f(x) − c, shift the graph of y = f(x) a distance c units downward
y = f(x − c), shift the graph of y = f(x) a distance c units to the right
y = f(x + c), shift the graph of y = f(x) a distance c units to the left
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 24 / 31
43. Now try these
y = sin (2x)
y = 2 sin (x)
y = e−x
y = −ex
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 25 / 31
44. Scaling and flipping
To obtain the graph of
y = f(c · x), scale the graph of f by c
y = c · f(x), scale the graph of f by c
If |c| < 1, the scaling is a
If c < 0, the scaling includes a
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 26 / 31
45. Scaling and flipping
To obtain the graph of
y = f(c · x), scale the graph of f horizontally by c
y = c · f(x), scale the graph of f by c
If |c| < 1, the scaling is a
If c < 0, the scaling includes a
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 26 / 31
46. Scaling and flipping
To obtain the graph of
y = f(c · x), scale the graph of f horizontally by c
y = c · f(x), scale the graph of f vertically by c
If |c| < 1, the scaling is a
If c < 0, the scaling includes a
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 26 / 31
47. Scaling and flipping
To obtain the graph of
y = f(c · x), scale the graph of f horizontally by c
y = c · f(x), scale the graph of f vertically by c
If |c| < 1, the scaling is a compression
If c < 0, the scaling includes a
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 26 / 31
48. Scaling and flipping
To obtain the graph of
y = f(c · x), scale the graph of f horizontally by c
y = c · f(x), scale the graph of f vertically by c
If |c| < 1, the scaling is a compression
If c < 0, the scaling includes a flip
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 26 / 31
49. Outline
Linear functions
Other Polynomial functions
Other power functions
Rational functions
Trigonometric Functions
Exponential and Logarithmic functions
Transformations of Functions
Compositions of Functions
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 27 / 31
50. Composition is a compounding of functions in
succession
g
. ◦f
.
x
. f
. . g
. . g ◦ f)(x)
(
f
.(x)
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 28 / 31
51. Composing
Example
Let f(x) = x2 and g(x) = sin x. Compute f ◦ g and g ◦ f.
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 29 / 31
52. Composing
Example
Let f(x) = x2 and g(x) = sin x. Compute f ◦ g and g ◦ f.
Solution
f ◦ g(x) = sin2 x while g ◦ f(x) = sin(x2 ). Note they are not the same.
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 29 / 31
53. Decomposing
Example
√
Express x2 − 4 as a composition of two functions. What is its
domain?
Solution
√
We can write the expression as f ◦ g, where f(u) = u and
g(x) = x2 − 4. The range of g needs to be within the domain of f. To
insure that x2 − 4 ≥ 0, we must have x ≤ −2 or x ≥ 2.
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 30 / 31
54. Summary
There are many classes of algebraic functions
Algebraic rules can be used to sketch graphs
. . . . . .
V63.0121.021/041, Calculus I (NYU) Section 2.2 Essential Functions September 8, 2010 31 / 31