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8/13/2019 Continuity 1401 x
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Worksheet Name:________________________________________
A functionfis continuous at a pointx = cif the graph offhas no gap, break, split, holes, jumps,
or a missing point forf(x) at the pointx = c. In addition, a functionfis continuous at a pointx = cif you can move along the graph of fthrough the point (c, f(c)) with a pencil without lifting
the pencil from the paper.
If a functionfis continuous at a pointx = c, then thecx
limf(x) must exists and its value must
eual f(c).
!or a function to be continuous at the pointx = c, the function must have a value atx = c(which
is f(c)) and thecx
limf(x) must have a value which is thesame asthe value of the function atx =
c. In general, a function is said to be continuous on the interval "a, b# if it is continuous at each
point in the interval.
It is important to understand what it means to say thatcx
limf(x) exists.
$%&&' ichael Aryee continuity age *
The concept of continuity
A function fis continuous at a pointx = cif all of the following conditions are fulfilled+
*. f(c ) is defined (this is means that the value of f(c) is not missing or undefined).
%.cx
limf(x) exists, (this is means that the value ofcx
limf(x) is not missing or
undefined),
and
.cx
limf(x) f(c) (this is means that the limit,cx
lim f(x), exists and its value is eual
to f(c))
cx
limf(x) exists if the following all of the following statements are true
*. cx
limf(x) is definite and has a value.
%. +cx
lim f(x) is definite and has a value.
. cx
limf(x)  +cx
lim f(x).
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When a function is not defined at certain values, these values are certainly the points of
discontinuity of the function. /ecause division by 0ero is not allowed in mathematics, anynumber or numbers that when substituted into the function causes the denominator to be 0ero,
thus making the function undefined, represent points of discontinuity.
1e usually concentrate only on either the domain of the function or the endpoints of the interval
making the domain.
2here are two main categories of discontinuity+ removableand nonremovable. 3on4removable
usually occurs where the graph has a break in it. 5ome people refer to this kind of discontinuityasjump discontinuity.
$%&&' ichael Aryee continuity age %
Points of discontinuity
Eample of discontinuity
A functionfis discontinuousat a pointx = cif one of the following conditions are fulfilled+
*. f(c ) is not defined at c,
%.cx
limf(x) does not exist, or
.cx
limf(x) f(c), (this is the case where the limit,cx
limf(x), exists but not eual to f(c))
A function is said to be discontinuousatx = c, if a hole, gap, or break occurs in the graph at
x = c, meaning the function violates one of the three items above.
o A nonremovable discontinuityis the situation where we are unableto find a value
forcx
limf(x) (that is,cx
limf(x) is not defined at c).
o A removable discontinuityis the situation where
*. 1e are able to find a value forcx
limf(x), in this casecx
limf(x) exists, but we
are unableto find a value for f(c), or
%. 1e are able to get values for bothcx
limf(x) and f(c), however, their values do
not match, that is,cx
limf(x) f(c).
The criterion for deciding whether a function is removable or irremovable is based on
whether the limit of the function at the point in question exists or does not exist.
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6iven the graph off(x)shown below determine iff(x)is continuous at a)x=& and b) x=*.
a) atx=&
!efthand !imit "i#hthand !imit T$osided !imit %alue of &unction
&limx
f(x)  & +&
limx
f(x)  &
!rom 7eft4hand and 8ight
hand we conclude that+
&limx
f(x)  &
Atx=&,
f(&)  *
'onclusion:5ince the limit at the point and the function value at that point are not eual, the
function isn9t continuous at that point. 2he function is discontinuous at x  &. 2hat is,&
limx
f(x)
f(&). 2his type of discontinuity is called removable since the limit exists. It is called
removable discontinuity because we can make the discontinuity to disappear by changing thevalue offat the point in uestion. 2hat is, we can change the value of f(c) to resolve the problem.
:n a graph, a removable discontinuity can be identified by a hole punched in the graph.
b) atx=*
!efthand !imit "i#hthand !imit T$osided !imit %alue of &unction
*limx
f(x)  * +
*limx
f(x)  &
!rom 7eft4hand and 8ight
hand we conclude that+
*limx
f(x)  (oes Not
Eist
Atx=*,
f(*)  *
'onclusion:5ince the limit at the point and the function value at that point are not eual, the
function isn9t continuous at that point. 2he function is discontinuous at x  *. 2hat is,&
limx
f(x)
f(&). 2his type of discontinuity is nonremovablesince the limit does not exist.
$%&&' ichael Aryee continuity age
Another eample of discontinuity
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;etermine whether the given function is continuous.
f(x) 
+ ,%
,
x
x
*
*
>
x
x
2he domain of this function is all real numbers. 2his is just one function, but it has differentdescription in different parts of the domain.
:ur task is to look for points of discontinuity. 2hese points may represent a value for which thedefinition of the function changes (in this particular case at x  *) or values that causes the
denominator to be 0ero).
1e call such values suspicious points. Always check for continuity at these suspicious points.
In this problem x  * is a suspicious point, and we must check for continuity at this point.
!efthand !imit "i#hthand !imit T$osided !imit %alue of &unction
*
limx f(x) 
*
limx
x

+
*
limx f(x) 
+
*
limx
%x
 '
!rom 7eft4hand and 8ight
hand we conclude that+
&limx
f(x)  (oes Not
Eist
Atx=*,
f(*)  (*) 
'onclusion:5ince the limit at the point and the function value at that point are not eual, the
function isn9t continuous at that point. 2he function is discontinuous at x  *.
2hat is,&
limx
f(x) f(*). 2his type of discontinuity is non4removable since the limit does not
exist.
$%&&' ichael Aryee continuity age
8/13/2019 Continuity 1401 x
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;etermine whether the given function is continuous.
f(x) 
+ ,*%
,
x
x
*
*
>
x
x
2he domain of this function is all real numbers. 2his is just one function, but it has differentdescription in different parts of the domain.
:ur task is to look for points of discontinuity. 2hese points may represent a value for which the
definition of the function changes (in this particular case at x  *) or values that causes thedenominator to be 0ero).
1e call such values suspicious points. Always check for continuity at these suspicious points.
In this problem x  * is a suspicious point, and we must check for continuity at this point.
!efthand !imit "i#hthand !imit T$osided !imit %alue of &unction
*limx
f(x) 
*limx
x

+*limx
f(x) +
*limx
%x*

!rom 7eft4hand and 8ighthand we conclude that+
*limx
f(x) 
Atx=*,
f(*)  (*) 
'onclusion: 5ince the limit at the point and the function value at that point are eual, the
function is continuous at that point. 2he function is continuous at x  *.
2hat is,*
limx
f(x) f(*).
$%&&' ichael Aryee continuity age '
An eample of a continuous function
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5tate whether the function is continuous at all points. 6ive the points of discontinuity, if any.
7et f(x) 
=
+
% x,=
%x,%
*&%
x
xx
In this problem x  % is a suspicious point, and we must check for continuity at this point.
2he domain of this function is all real numbers.
!efthand !imit "i#hthand !imit T$osided !imit %alue of
&unction
%limx
f(x) 
%limx
%
*&,%
+
x
xx

%limx
)%(
)')(%(
+
x
xx

%limx
(x > ')  =
5ame as 7eft4hand
limit+
+%
limx
f(x)  =
!rom 7eft4hand and
8ight hand weconclude that+
%limx
f(x)  =
Atx=%,
f(%)  =
'onclusion:5ince the limit at the point x  % and the function value at that point are eual, thefunction is continuous at that point. 2he function is continuous at x  %.
2hat is,%
limx
f(x) f(%).
$%&&' ichael Aryee continuity age ?
An eample of a continuous function
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1here is the function f(x)  @ x % @ continuousB
)olution:
2he given function is the same as f(x) 
),%(,%
x
x
%
%