section 5.2 – applications of the second derivative
TRANSCRIPT
Section 5.2 – Applications of the Second Derivative
THE SECOND DERIVATIVE TEST FOR MAX/MIN
If f ' a 0 and , then f a is a .
I
f " a 0 minimum
ff f ' a 0 and , then f a is a" a 0 maximum.
Theory First….POINT OF INFLECTION
If f" a 0 and f " a changes from pos to neg or neg to pos,
a point of inflection exists at x = a
TEST FOR CONCAVITY
If f" a f is concave at x = a
If f" a f is con
0 up
0 docave at xwn = a
3 2If f x x 5x 3x, then the graph of f is decreasing
and concave down on the interval
1 1 2 1 5 5A. 0, B. , C. , D. ,3 E. 3,
3 3 3 3 3 3
2f ' x 3x 10x 3
0 3x 1 x 3
1x , 3
3
1
33
+ _ +
X X
f " x 6x 10
0 6x 10
5x
3
5
3
_ +
2
Suppose a function f is defined so that it has derivatives
f ' x x 1 x and f " x x 2 3x . Over which interval
is the graph of f both increasing and concave up?
2 2A. x 0 B. 0 x C. x 1 D. x 1 E. none of thes
3 3
e
0 1
+ + _
X
0 2
3
_ + _
3 2Find the maximum value of f x 2x 3x 12x 4 on
the closed interval [0, 2]. Justify your answer.
2f ' x 6x 6x 12
0 6 x 2 x 1
x 2,1
f " x 12x 6
f " 2 0
f " 1 0
Since f ‘ (-2) = 0 and f “ (-2) < 0 there is a relative max at x = -2,but x = -2 is not on the interval [0, 2]
f 0 4 f 2 8 Since f(2) > f(0), the abs max occurs at x = 2
The maximum value is 8
2 3
Find the x-coordinates of the point(s) of inflection of the
function f if f ' x x 2 x 7 . Justify your answer.
3 2 2f " x 2 x 2 x 7 3 x 7 x 2
2f " x x 2 x 7 2 x 7 3 x 2
20 x 2 x 7 5x 20
2 4 7
+ _ + +
x = 2 since f “ (x) changes from pos to neg.
x = 4 since f “ (x) changes from neg to pos.
2
Which of the following are true about the function f if its
derivative is defined by f ' x x 1 4 x ?
I. f is decreasing for all x < 4.
II. f has a local maximum at x = 1.
III. f is concave up for all 1
< x < 3.
A. I only B. II only C. III only D. II and III only E. I, II, III
1 4
+ + _
XX
2f " x 2 x 1 4 x 1 x 1
f " x x 1 2 4 x 1 x 1
0 x 1 9 3x x 1, 3
f " 2 0
2
The number of inflection points for the graph of
y 2x cos x in the interval [0, 5] is:
A. 6 B. 7 C. 8 D. 9 E. 10
X
CALCULATOR REQUIRED
CALCULATOR REQUIRED
x 2
Suppose the continuous function f is defined on the closed
interval [0, 3] such that its derivative f ' is defined by
f ' x e sin x 1. Which of the following are true about
the graph of f?
I. f has exa
ctly one relative maximum point.
II. f has two relative minimum points.
III. f has two inflection points.
A. I only B. II only C. III only D. I and II only E. I, II, III
dy
dx
2
2
d y
dx
2
The position at time t > 0 of a particle moving on the x-axis
is given by x t sin tcos t. At the first instant when the
acceleration is 1 unit per sec , the particle has velocity
A. -1 units per sec
B.
-0.866 units per sec
C. 0 units per sec
D. 0.866 units per sec
E. 1 unit per sec
x t sin tcos t
x t sin t1
t22
cos
1x t sin2t
2
v t cos2t a t 2sin2t
1 2sin2t1
sin2t2
c3
2os2t
CALCULATOR REQUIRED
4 5x x
Consider the function f x . Find the value of x for2 10
which the derivative of f attains its maximum. Justify your answer.
4
3 xf ' x 2x
2
2 3f " x 6x 2x
20 2x 3 x x 0, 3
2f "' x 12x 6x
f "' x 6x 2 x
0 0f "' 6 2 0 0
3 3f "' 6 2 3 0
Since f " 3 0 and f "' 3 0, the derivative of f achieves
a maximum at x = 3
NO CALCULATOR
2Which of the following is true about the graph of f x ln x 4
in the interval -2, 2 ?
A. f is increasing
B. f attains a relative minimum at (0, 0)
C. f has a range of all real numbers
D. f is concave down
E. f has an asymptote at x = 0
2 2On 2, 2 , f x ln x 4 ln 4 x
2
2xf ' x
4 x
X
2
22
2 4 x 2x 2xf " x
4 x
22
2 22 2
2 x 42x 8
4 x 4 x
X
X
3 2Let f x x px qx.
a Find the values of p and q so that f 1 8 and f ' 1 12
b Find the values of p so that the graph of f changes concavity
at x = 2
(c) Under what conditions of p and q will the graph of
f be
increasing everywhere? (BC only)
3 2Let f x x px qx.
a Find the values of p and q so that f 1 8 and f ' 1 12
p 81 qf 1 2f ' x 3x 2px q
3 2p q 2' 1f 1
p q 7
2p q 9p 2, q 5
3 2Let f x x px qx.
b Find the values of p so that the graph of f changes concavity
at x = 2
2f ' x 3x 2px q
f " x 6x 2p
f " 2 6 2 2p
0 12 2p
p 6
3 2Let f x x px qx.
(c) Under what conditions of p and q will the graph of f be
increasing everywhere?
2f ' x 3x 2px q
22p 4 3 q 0
24p 12q 0 24p 12q2p 3q
4 2Let f x x ax b. The graph of f has a relative maximum
at (0, 1) and an inflection point when x = 1. Find the values of
a and b.
3f ' x 4x 2ax
2f " x 12x 2a
20 12 1 2a a 6
4 2f x x 6x b
4 21 0 6 0 b
b 1
CALCULATOR REQUIRED
2
dy cos xIf f(x) is defined on - x and , which of the
dx x 1following statements about the graph of y f x is true?
A. The graph has no relative extremum.
B. The graph has one point of inflection and two
relative extrema.
C. The graph has two points of inflection and one relative extremum.
D. The graph has two points of inflection and two relative extrema.
E. The graph has three points of inflection and two relative extrema.
X
X
dy
dx
2
2
d y
dx