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Chapter 2: Answers 2 Jack K. Cohen Colorado School of Mines
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;SPMlt;LI;SPMgt;;SPMlt;PRE;SPMgt;
f[x_] := x^3 + 3x^2
f[2]
20
f[x] /. x -;SPMamp;gt; 2
20
f[t]
2 3
3 t + t
f[cat]
2 3
3 cat + cat
Table[f[n], <#1#>n, 1, 5<#1#>]
<#2#>4, 20, 54, 112, 200<#2#>
Plot[f[x], <#3#>x, -2, 2<#3#>]
See Figure 1.
;SPMlt;/PRE;SPMgt;
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;SPMlt;DIV class=;SPMquot;CENTER;SPMquot;;SPMgt;;SPMlt;A ID=;SPMquot;10;SPMquot;;SPMgt;;SPMlt;/A;SPMgt;
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;SPMlt;CAPTION class=;SPMquot;BOTTOM;SPMquot;;SPMgt;;SPMlt;STRONG;SPMgt;Figure:;SPMlt;/STRONG;SPMgt;
Plot of ;SPMlt;!-- MATH
#math1#x3 +3x2
--;SPMgt;
;SPMlt;I;SPMgt;x;SPMlt;/I;SPMgt;;SPMlt;SUP;SPMgt;3;SPMlt;/SUP;SPMgt; +3;SPMlt;I;SPMgt;x;SPMlt;/I;SPMgt;;SPMlt;SUP;SPMgt;2;SPMlt;/SUP;SPMgt;.;SPMlt;/CAPTION;SPMgt;
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#figure4#
;SPMquot;;SPMgt;;SPMlt;/TD;SPMgt;;SPMlt;/TR;SPMgt;
;SPMlt;/TABLE;SPMgt;
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;SPMlt;/LI;SPMgt;
;SPMlt;LI;SPMgt;;SPMlt;!-- MATH
#math2##tex2html_wrap_inline281#
--;SPMgt;
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STYLE=;SPMquot;height: 179.22ex; vertical-align: -0.68ex; ;SPMquot; SRC=;SPMquot;img2.png;SPMquot;
ALT=;SPMquot;#math3##tex2html_wrap_inline283#;SPMquot;;SPMgt; ;SPMlt;FONT SIZE=;SPMquot;+2;SPMquot;;SPMgt;;SPMlt;!-- MATH
#math4##tex2html_wrap_inline285#
--;SPMgt;
;SPMlt;IMG
STYLE=;SPMquot;height: 2.30ex; vertical-align: 160.64ex; ;SPMquot; SRC=;SPMquot;img3.png;SPMquot;
ALT=;SPMquot;#math5##tex2html_wrap_inline287#;SPMquot;;SPMgt;;SPMlt;/FONT;SPMgt; is 1/10.
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;SPMlt;LI;SPMgt;Figure 3 shows the output from
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Plot[(Sqrt[x + 25] - 5)/x, <#14#>x, -2, 2<#14#>, PlotRange -;SPMamp;gt; <#15#>0, .5<#15#>]
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;SPMlt;DIV class=;SPMquot;CENTER;SPMquot;;SPMgt;;SPMlt;A ID=;SPMquot;19;SPMquot;;SPMgt;;SPMlt;/A;SPMgt;
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;SPMlt;CAPTION class=;SPMquot;BOTTOM;SPMquot;;SPMgt;;SPMlt;STRONG;SPMgt;Figure:;SPMlt;/STRONG;SPMgt;
Plot for problem 2.;SPMlt;/CAPTION;SPMgt;
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#figure16#
;SPMquot;;SPMgt;;SPMlt;/TD;SPMgt;;SPMlt;/TR;SPMgt;
;SPMlt;/TABLE;SPMgt;
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;SPMlt;LI;SPMgt;Here is the output from
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Table[<#19#>x, (Sqrt[x + 25] - 5)/x<#19#>, <#20#>x, -1/5, 1/5, 1/20<#20#>] //N //TableForm
;SPMlt;PRE;SPMgt;
-0.2 0.100201
-0.15 0.10015
-0.1 0.1001
-0.05 0.10005
0 Indeterminate
0.05 0.09995
0.1 0.0999002
0.15 0.0998504
0.2 0.0998008
;SPMlt;/PRE;SPMgt;
It may seem more natural to ``force'' to use decimal arithmetic during the calculation instead of evoking N afterwards, perhaps like this:
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Table[<#21#>x, (Sqrt[x + 25] - 5)/x<#21#>, <#22#>x, -.2, .2, .05<#22#>] //TableForm.
;SPMlt;P;SPMgt;
However, with in-exact arithmetic, the user has to be alert enough to reject output that is too close to the singular point:
;SPMlt;PRE;SPMgt;
-0.2 0.100201
-0.15 0.10015
-0.1 0.1001
-0.05 0.10005
-17
-1.38778 10 0.
0.05 0.09995
0.1 0.0999002
0.15 0.0998504
0.2 0.0998008
;SPMlt;/PRE;SPMgt;
;SPMlt;P;SPMgt;
;SPMlt;/LI;SPMgt;
;SPMlt;LI;SPMgt;If Example 12 seems obscure, ask your instructor for help.
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;SPMlt;LI;SPMgt;As indicated, ;SPMlt;!-- MATH
#math6##tex2html_wrap_inline289# #tex2html_wrap_inline290# 5 + x/10
--;SPMgt;
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ALT=;SPMquot;#tex2html_wrap_inline294#;SPMquot;;SPMgt; 5 + ;SPMlt;I;SPMgt;x;SPMlt;/I;SPMgt;/10, so we can replace the given limit by ;SPMlt;!-- MATH
#math8##tex2html_wrap_inline296#
--;SPMgt;
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ALT=;SPMquot;#math9##tex2html_wrap_inline298#;SPMquot;;SPMgt; ;SPMlt;FONT SIZE=;SPMquot;+2;SPMquot;;SPMgt;;SPMlt;!-- MATH
#math10##tex2html_wrap_inline300#
--;SPMgt;
;SPMlt;IMG
STYLE=;SPMquot;height: 1.02ex; vertical-align: 161.92ex; ;SPMquot; SRC=;SPMquot;img7.png;SPMquot;
ALT=;SPMquot;#math11##tex2html_wrap_inline302#;SPMquot;;SPMgt;;SPMlt;/FONT;SPMgt; = 1/10.
;SPMlt;/LI;SPMgt;
;SPMlt;LI;SPMgt;Running the indicated code gives:
;SPMlt;PRE;SPMgt;
0.1 0.0999002
0.01 0.09999
0.001 0.099999
0.0001 0.0999999
0.00001 0.1
;SPMlt;/PRE;SPMgt;
With x -;SPMamp;gt; a - 1/10;SPMamp;#710;k, we get:
;SPMlt;PRE;SPMgt;
-0.1 0.1001
-0.01 0.10001
-0.001 0.100001
-0.0001 0.1
-0.00001 0.1
;SPMlt;/PRE;SPMgt;
;SPMlt;P;SPMgt;
Note: We have supplied a function called LimitTable that uses this code as its core.
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;SPMlt;/LI;SPMgt;
;SPMlt;LI;SPMgt;Your opinion is more important than mine.
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;SPMlt;/OL;SPMgt;
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;SPMlt;/LI;SPMgt;
;SPMlt;LI;SPMgt;(2.2.8) ;SPMlt;!-- MATH
#math12##tex2html_wrap_inline304#
--;SPMgt;
;SPMlt;IMG
STYLE=;SPMquot;height: 3.26ex; vertical-align: 159.85ex; ;SPMquot; SRC=;SPMquot;img8.png;SPMquot;
ALT=;SPMquot;#math13##tex2html_wrap_inline306#;SPMquot;;SPMgt; ;SPMlt;FONT SIZE=;SPMquot;+2;SPMquot;;SPMgt;;SPMlt;!-- MATH
#math14##tex2html_wrap_inline308#
--;SPMgt;
;SPMlt;IMG
STYLE=;SPMquot;height: 2.30ex; vertical-align: 160.42ex; ;SPMquot; SRC=;SPMquot;img9.png;SPMquot;
ALT=;SPMquot;#math15##tex2html_wrap_inline310#;SPMquot;;SPMgt;;SPMlt;/FONT;SPMgt; = 3/4.
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;SPMlt;/LI;SPMgt;
;SPMlt;LI;SPMgt;(2.2.22) ;SPMlt;!-- MATH
#math16##tex2html_wrap_inline312#
--;SPMgt;
;SPMlt;IMG
STYLE=;SPMquot;height: 3.32ex; vertical-align: 159.85ex; ;SPMquot; SRC=;SPMquot;img10.png;SPMquot;
ALT=;SPMquot;#math17##tex2html_wrap_inline314#;SPMquot;;SPMgt; ;SPMlt;FONT SIZE=;SPMquot;+2;SPMquot;;SPMgt;;SPMlt;!-- MATH
#math18##tex2html_wrap_inline316#
--;SPMgt;
;SPMlt;IMG
STYLE=;SPMquot;height: 2.30ex; vertical-align: 160.47ex; ;SPMquot; SRC=;SPMquot;img11.png;SPMquot;
ALT=;SPMquot;#math19##tex2html_wrap_inline318#;SPMquot;;SPMgt;;SPMlt;/FONT;SPMgt; = 1/6.
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;SPMlt;/LI;SPMgt;
;SPMlt;LI;SPMgt;(2.2.32) ;SPMlt;!-- MATH
#math20##tex2html_wrap_inline320#
--;SPMgt;
;SPMlt;IMG
STYLE=;SPMquot;height: 3.32ex; vertical-align: 159.79ex; ;SPMquot; SRC=;SPMquot;img12.png;SPMquot;
ALT=;SPMquot;#math21##tex2html_wrap_inline322#;SPMquot;;SPMgt; ;SPMlt;FONT SIZE=;SPMquot;+2;SPMquot;;SPMgt;;SPMlt;!-- MATH
#math22##tex2html_wrap_inline324#
--;SPMgt;
;SPMlt;IMG
STYLE=;SPMquot;height: 2.30ex; vertical-align: 160.47ex; ;SPMquot; SRC=;SPMquot;img13.png;SPMquot;
ALT=;SPMquot;#math23##tex2html_wrap_inline326#;SPMquot;;SPMgt;;SPMlt;/FONT;SPMgt; = 4.
;SPMlt;P;SPMgt;
;SPMlt;/LI;SPMgt;
;SPMlt;LI;SPMgt;(2.2.35) ;SPMlt;!-- MATH
#math24##tex2html_wrap_inline328#
--;SPMgt;
;SPMlt;IMG
STYLE=;SPMquot;height: 179.22ex; vertical-align: -0.68ex; ;SPMquot; SRC=;SPMquot;img2.png;SPMquot;
ALT=;SPMquot;#math25##tex2html_wrap_inline330#;SPMquot;;SPMgt; ;SPMlt;FONT SIZE=;SPMquot;+2;SPMquot;;SPMgt;;SPMlt;!-- MATH
#math26##tex2html_wrap_inline332##tex2html_wrap_inline333##tex2html_wrap_inline334# - #tex2html_wrap_inline335##tex2html_wrap_inline336#
--;SPMgt;
;SPMlt;IMG
STYLE=;SPMquot;height: 3.26ex; vertical-align: 159.69ex; ;SPMquot; SRC=;SPMquot;img14.png;SPMquot;
ALT=;SPMquot;#math27##tex2html_wrap_inline338#;SPMquot;;SPMgt;;SPMlt;IMG
STYLE=;SPMquot;height: 2.94ex; vertical-align: 159.48ex; ;SPMquot; SRC=;SPMquot;img15.png;SPMquot;
ALT=;SPMquot;#math28##tex2html_wrap_inline340##tex2html_wrap_inline341##tex2html_wrap_inline342#-#tex2html_wrap_inline343#;SPMquot;;SPMgt;;SPMlt;IMG
STYLE=;SPMquot;height: 3.90ex; vertical-align: 158.87ex; ;SPMquot; SRC=;SPMquot;img16.png;SPMquot;
ALT=;SPMquot;#math29##tex2html_wrap_inline345#;SPMquot;;SPMgt; - ;SPMlt;IMG
STYLE=;SPMquot;height: 3.07ex; vertical-align: 159.88ex; ;SPMquot; SRC=;SPMquot;img17.png;SPMquot;
ALT=;SPMquot;#math30##tex2html_wrap_inline347#;SPMquot;;SPMgt;;SPMlt;IMG
STYLE=;SPMquot;height: 2.94ex; vertical-align: 159.48ex; ;SPMquot; SRC=;SPMquot;img18.png;SPMquot;
ALT=;SPMquot;#math31##tex2html_wrap_inline349##tex2html_wrap_inline350##tex2html_wrap_inline351#-#tex2html_wrap_inline352##tex2html_wrap_inline353#;SPMquot;;SPMgt;;SPMlt;/FONT;SPMgt; = - 1/10.
;SPMlt;P;SPMgt;
;SPMlt;/LI;SPMgt;
;SPMlt;LI;SPMgt;(2.2.36) ;SPMlt;!-- MATH
#math32##tex2html_wrap_inline355#
--;SPMgt;
;SPMlt;IMG
STYLE=;SPMquot;height: 3.90ex; vertical-align: 159.27ex; ;SPMquot; SRC=;SPMquot;img19.png;SPMquot;
ALT=;SPMquot;#math33##tex2html_wrap_inline357#;SPMquot;;SPMgt; ;SPMlt;FONT SIZE=;SPMquot;+2;SPMquot;;SPMgt;;SPMlt;!-- MATH
#math34##tex2html_wrap_inline359#
--;SPMgt;
;SPMlt;IMG
STYLE=;SPMquot;height: 2.30ex; vertical-align: 160.47ex; ;SPMquot; SRC=;SPMquot;img20.png;SPMquot;
ALT=;SPMquot;#math35##tex2html_wrap_inline361#;SPMquot;;SPMgt;;SPMlt;/FONT;SPMgt; = 1/3.
To do this algebraically is a bit trickey. Factor the numerator: ;SPMlt;!-- MATH
#math36#(x1/3 -2)(x1/3 + 2)
--;SPMgt;
(;SPMlt;I;SPMgt;x;SPMlt;/I;SPMgt;;SPMlt;SUP;SPMgt;1/3;SPMlt;/SUP;SPMgt; -2)(;SPMlt;I;SPMgt;x;SPMlt;/I;SPMgt;;SPMlt;SUP;SPMgt;1/3;SPMlt;/SUP;SPMgt; + 2)
and the denominator: ;SPMlt;!-- MATH
#math37#(x1/3 -2)(x2/3 +2x1/3 + 4)
--;SPMgt;
(;SPMlt;I;SPMgt;x;SPMlt;/I;SPMgt;;SPMlt;SUP;SPMgt;1/3;SPMlt;/SUP;SPMgt; -2)(;SPMlt;I;SPMgt;x;SPMlt;/I;SPMgt;;SPMlt;SUP;SPMgt;2/3;SPMlt;/SUP;SPMgt; +2;SPMlt;I;SPMgt;x;SPMlt;/I;SPMgt;;SPMlt;SUP;SPMgt;1/3;SPMlt;/SUP;SPMgt; + 4). Then cancel the common
term and substitute ;SPMlt;I;SPMgt;x;SPMlt;/I;SPMgt; = 8.
;SPMlt;/LI;SPMgt;
;SPMlt;/OL;SPMgt;
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