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EXTREMA ON AN
INTERVAL
Section 3.1
When you are done with your
homework, you should be able
to…
• Understand the definition of
extrema of a function on an interval
• Understand the definition of relative
extrema of a function on an open
interval
• Find extrema on a closed interval
EXTREMA OF A FUNCTION
f  c2 
a
c1

c2

f  c1 
b
DEFINITION OF EXTREMA
Let f be defined on an open interval I
containing c.
1. f  c  is the minimum of f on I if
f  c   f  x  for all x in I.
2. f  c  is the maximum of f on I if
f  c   f  c  for all x in I.
EXTREMA CONTINUED…
• The minimum and maximum of a
function on an interval are the
extreme values, or extrema of the
function on the interval
• The singular form of extrema is
extremum
• The minimum and maximum of a
function on an interval are also called
the absolute minimum and absolute
maximum on the interval
EXTREMA CONTINUED…
• A function does not need to have a
maximum or minimum (see graph)
• Extrema that occur at endpoints of
an interval are called endpoint
extrema
f  x = x2
3
2
1
-2
2
THE EXTREME VALUE
THEOREM
If f is continuous on a closed interval
 a, b , then f has both a minimum
and a maximum on the interval.
DEFINITION OF RELATIVE
EXTREMA
1. If there is an open interval containing
c on which f  c  is a maximum, then f  c 
is called a relative maximum of f, or
you can say that f has a relative
maximum at c, f  c  .
2. If there is an open interval containing
c on which f is a minimum, then f  c  is
called a relative minimum of f, or you
can say that f has a relative minimum
at c, f  c  .




Find the value of the
derivative (if it exists) at
the indicated extremum.
x
f  x   cos ;  2, 1
2
0.0
0.0
Find the value of the
derivative (if it exists) at
the indicated extremum.
 2 2 3
r  s   3s s  1;   ,

 3 3 
0.0
0.0
Find the value of the
derivative (if it exists) at
the indicated extremum.
f  x   4  x ;  0, 4
f  x  f c
f   x   lim
x c
xc
4 x 4
f  x   f  0

lim
 lim
1
x 0
x 0
x0
x
4 x 4
f  x   f  0

lim
 lim
 1
x 0
x 0
x0
x
Therefore, f   0  does not exist
DEFINITION OF A CRITICAL
NUMBER
Let f be defined at c.
1. If f '  c   0, then c is a critical
number of f.
2. If f is not differentiable at c, then c
is a critical number of f.
Locate the critical
numbers of the
function.
A.
c  2
B. c  2, c  0
C. c  2, c  0
D. None of these
x 4
f  x 
x
2
Locate the critical numbers of the
function.
f    2sec  tan  ,  0, 2 

3
7
11
, c
, c
A. c  , c 
2
2
6
6
7
11
, c
B. c 
6
6
4
5
C. c 
, c
3
3
D. None of these
THEOREM: RELATIVE EXTREMA
OCCUR ONLY AT CRITICAL
NUMBERS
If f has a relative maximum or minimum at
x  c, then c is a critical number of
f.
GUIDELINES FOR FINDING
EXTREMA ON A CLOSED
INTERVAL
To find the extrema of a continuous function
f on a closed interval  a, b, use the
following steps.
1. Find the critical numbers of f in c.
2. Evaluate f at each critical number in  a, b .
3. Evaluate f at each endpoint of  a, b .
4. The least of these outputs is the
minimum. The greatest is the maximum.
The maximum of a function
that is continuous on a
closed interval can occur at
two different values in the
interval.
A. True
B. False