{VERSION 2 3 "IBM INTEL NT" "2.3" } {USTYLETAB {CSTYLE "Maple Input" -1 0 "Courier" 0 1 255 0 0 1 0 1 0 0 1 0 0 0 0 }{CSTYLE "2D Math" -1 2 "Times" 0 1 0 0 0 0 0 0 2 0 0 0 0 0 0 }{CSTYLE "2D Comment" 2 18 "" 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 } {CSTYLE "" -1 256 "" 0 1 0 0 176 0 1 1 0 0 0 0 0 0 0 }{CSTYLE "" -1 257 "" 0 1 0 0 2 0 1 0 0 0 0 0 0 0 0 }{CSTYLE "" -1 258 "" 0 1 0 0 3 0 1 0 0 0 0 0 0 0 0 }{CSTYLE "" -1 259 "" 0 1 0 0 2 0 0 1 0 0 0 0 0 0 0 }{CSTYLE "" -1 260 "" 1 14 0 0 20 0 0 0 0 0 0 0 0 0 0 }{CSTYLE "" -1 261 "" 1 14 0 0 7 0 0 0 0 0 0 0 0 0 0 }{CSTYLE "" -1 262 "" 1 14 0 0 20 0 0 1 0 0 0 0 0 0 0 }{CSTYLE "" -1 263 "" 1 14 0 0 0 0 0 1 0 0 0 0 0 0 0 }{CSTYLE "" -1 264 "" 0 1 0 0 0 0 0 1 0 0 0 0 0 0 0 }{CSTYLE " " -1 265 "" 0 1 115 99 152 0 0 1 0 0 0 0 0 0 0 }{CSTYLE "" -1 266 "" 0 1 0 0 0 0 0 1 0 0 0 0 0 0 0 }{CSTYLE "" -1 267 "" 1 14 0 0 0 0 0 0 0 0 0 0 0 0 0 }{CSTYLE "" -1 268 "" 0 1 237 1 100 0 1 0 0 0 0 0 0 0 0 }{PSTYLE "Normal" -1 0 1 {CSTYLE "" -1 -1 "Times" 1 12 0 0 0 1 2 2 2 2 2 2 1 1 1 }1 1 0 0 0 0 1 0 1 0 2 2 0 1 }} {SECT 0 {PARA 0 "" 0 "" {TEXT 260 1 "(" }{TEXT 262 1 "1" }{TEXT 261 3 ") " }{TEXT 258 34 "Si calcolino tutte le primitive di" }{TEXT 256 1 " " }{TEXT -1 2 " " }{XPPEDIT 18 0 "f := x->1/(x^2-x)" ">%\"fG:6#%\"x G7\"6$%)operatorG%&arrowG6\"*&\"\"\"\"\"\",&*$F&\"\"#F.F&!\"\"F2F+F+" }{TEXT -1 2 " " }{TEXT 257 65 "per x in (0, 1) e si determini la prim itiva F tale che F(1/2) = 0" }{TEXT -1 47 ".\nPotremmo usare direttame nte Maple e ottenere;" }}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 16 "f:= x->1/(x^2-x);" }}}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 26 "Int(f(x),x ) = int(f(x),x);" }}}{PARA 0 "" 0 "" {TEXT 259 2 "ma" }{TEXT -1 246 " \+ in casi come questo, in cui f(x) \350 definito in un'uniione di interv alli, occorre stare attenti: potrebbe produrre primitive buone su uno \+ e non su tutti.\nControlliamo a mano (e, comunque, in un compito dobbi amo giustificare l'intergale ottenuto):" }}{PARA 0 "" 0 "" {TEXT -1 121 "idea: cerco di espriemere l'integranda come somma di frazioni ave nti per denominatore i fattori del denominatore attuale:" }}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 55 "a/x+b/(x-1)=1/(x^2-x); simplify(a/x +b/(x-1)=1/(x^2-x));" }}}{PARA 0 "" 0 "" {TEXT -1 43 "Posso prendere \+ a = -1 e b = 1. Verifica:" }}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 23 "simplify(-1/x+1/(x-1));" }}}{PARA 0 "" 0 "" {TEXT -1 6 " OK " } {XPPEDIT 18 0 "int(f(x),x) = int(-1/x+1/(x-1),x)" "/-%$intG6$-%\"fG6#% \"xGF)-F$6$,&*&\"\"\"\"\"\"F)!\"\"F0*&\"\"\"F/,&F)F/\"\"\"F0F0F/F)" } {TEXT -1 169 " \n\nSo che le primitive di 1/t hanno la forma log(t)+c1 per t > 0 e log(-t)+c2 per t < 0.\nPer x in (0,1) x > 0 e x-1 \+ < 0, per cui, a meno di costanti additive,\n " }{XPPEDIT 18 0 "int(1 /x,x) = log(x)" "/-%$intG6$*&\"\"\"\"\"\"%\"xG!\"\"F)-%$logG6#F)" } {TEXT -1 7 " e " }{XPPEDIT 18 0 "int(1/(x-1),x) = log(1-x)" "/-%$i ntG6$*&\"\"\"\"\"\",&%\"xGF(\"\"\"!\"\"F,F*-%$logG6#,&\"\"\"F(F*F," } {TEXT -1 10 " \nQuindi " }{XPPEDIT 18 0 "int(f(x),x) = -ln(x)+ln(1-x) " "/-%$intG6$-%\"fG6#%\"xGF),&-%#lnG6#F)!\"\"-F,6#,&\"\"\"\"\"\"F)F.F3 " }{TEXT -1 69 " ( +c)\nOra cerco F(x) = -log(x) + log(1-x) + c tal e che F(1/2) = 0" }}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 36 "solve(-l og(1/2)+log(1-1/2)+c = 0,c);" }}}{PARA 0 "" 0 "" {TEXT -1 40 " F(x) = \+ -log(x) - log(1-x). Verifica:" }}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 59 "F := x -> -log(x)+log(1-x): F(1/2); simplify(diff(F(x),x));" } }}{PARA 0 "" 0 "" {TEXT -1 2 "OK" }}{PARA 0 "" 0 "" {TEXT -1 25 "----- -------------------\n" }{TEXT 263 4 "(2) " }{TEXT 267 1 " " }{TEXT 268 34 "Si calcolino al variare di x in R:" }{TEXT -1 6 "\n(a) " } {XPPEDIT 18 0 "int(abs(t^2-1),t=2..x)" "-%$intG6$-%$absG6#,&*$%\"tG\" \"#\"\"\"\"\"\"!\"\"/F*;\"\"#%\"xG" }{TEXT -1 13 " e (b) " } {XPPEDIT 18 0 "int(1/(t^2+9),t=0..x)" "-%$intG6$*&\"\"\"\"\"\",&*$%\"t G\"\"#F'\"\"*F'!\"\"/F*;\"\"!%\"xG" }{TEXT -1 2 " " }}{PARA 0 "" 0 " " {TEXT -1 1 "(" }{TEXT 266 1 "a" }{TEXT -1 40 ") Pensiamo l'andament o dell'integranda:" }}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 36 "f:= t \+ -> abs(t^2-1): plot (f,-3..3);" }}}{PARA 0 "" 0 "" {TEXT -1 12 "Per x \+ >= 1 " }}{PARA 0 "" 0 "" {XPPEDIT 18 0 "int(abs(t^2-1),t=2..x) = int( t^2-1,t=2..x) " "/-%$intG6$-%$absG6#,&*$%\"tG\"\"#\"\"\"\"\"\"!\"\"/F+ ;\"\"#%\"xG-F$6$,&*$F+\"\"#F-\"\"\"F//F+;\"\"#F3" }{TEXT -1 3 " = " } {XPPEDIT 18 0 "x^3/3-x-2/3" ",(*&%\"xG\"\"$\"\"$!\"\"\"\"\"F$F'*&\"\"# F(\"\"$F'F'" }}{PARA 0 "" 0 "" {TEXT -1 44 "in quanto t varia in un in tervallo in cui " }{XPPEDIT 18 0 "abs(t^2-1)= t^2-1" "/-%$absG6#,&*$ %\"tG\"\"#\"\"\"\"\"\"!\"\",&*$F(\"\"#F*\"\"\"F," }{TEXT -1 20 " \nPe r x in [-1,1]\n" }{XPPEDIT 18 0 "int(abs(t^2-1),t=2..x) = int(abs(t^2 -1),t=2..1)+int(abs(t^2-1),t=1..x) " "/-%$intG6$-%$absG6#,&*$%\"tG\"\" #\"\"\"\"\"\"!\"\"/F+;\"\"#%\"xG,&-F$6$-F'6#,&*$F+\"\"#F-\"\"\"F//F+; \"\"#\"\"\"F--F$6$-F'6#,&*$F+\"\"#F-\"\"\"F//F+;\"\"\"F3F-" }{TEXT -1 4 " = " }{XPPEDIT 18 0 "1^3/3-1-2/3 + int(-t^2+1,t=1..x)" ",**&\"\"\" \"\"$\"\"$!\"\"\"\"\"\"\"\"F'*&\"\"#F(\"\"$F'F'-%$intG6$,&*$%\"tG\"\"# F'\"\"\"F(/F2;\"\"\"%\"xGF(" }{TEXT -1 3 "\n= " }{XPPEDIT 18 0 "1/3-1- 2/3-x^3/3+x-2/3" ",.*&\"\"\"\"\"\"\"\"$!\"\"F%\"\"\"F'*&\"\"#F%\"\"$F' F'*&%\"xG\"\"$\"\"$F'F'F-F%*&\"\"#F%\"\"$F'F'" }{TEXT -1 3 " = " } {XPPEDIT 18 0 "x-x^3/3-2" ",(%\"xG\"\"\"*&F#\"\"$\"\"$!\"\"F(\"\"#F(" }{TEXT -1 86 "\nAbbiamo separato quanto accade per t tra 2 e 1 e per t che varia in [-1,1], in cui " }{XPPEDIT 18 0 "abs(t^2-1)=-(t^2-1)" "/-%$absG6#,&*$%\"tG\"\"#\"\"\"\"\"\"!\"\",$,&*$F(\"\"#F*\"\"\"F,F," } {TEXT -1 13 "\nPer x <= -1\n" }{XPPEDIT 18 0 "int(abs(t^2-1),t=2..x) = int(abs(t^2-1),t=2..1)+int(abs(t^2-1),t=1..-1) +int(abs(t^2-1),t=-1.. x) " "/-%$intG6$-%$absG6#,&*$%\"tG\"\"#\"\"\"\"\"\"!\"\"/F+;\"\"#%\"xG ,(-F$6$-F'6#,&*$F+\"\"#F-\"\"\"F//F+;\"\"#\"\"\"F--F$6$-F'6#,&*$F+\"\" #F-\"\"\"F//F+;\"\"\",$\"\"\"F/F--F$6$-F'6#,&*$F+\"\"#F-\"\"\"F//F+;,$ \"\"\"F/F3F-" }{TEXT -1 6 " \n= " }{XPPEDIT 18 0 "1^3/3-1-2/3 + (-1) - (-1)^3/3-2 + int(t^2-1,t=-1..x)" ",0*&\"\"\"\"\"$\"\"$!\"\"\"\"\" \"\"\"F'*&\"\"#F(\"\"$F'F',$\"\"\"F'F(*&,$\"\"\"F'\"\"$\"\"$F'F'\"\"#F '-%$intG6$,&*$%\"tG\"\"#F(\"\"\"F'/F:;,$\"\"\"F'%\"xGF(" }{TEXT -1 4 " \n= " }{XPPEDIT 18 0 "-4+x^3/3-x-2/3" ",*\"\"%!\"\"*&%\"xG\"\"$\"\"$F $\"\"\"F&F$*&\"\"#F)\"\"$F$F$" }{TEXT -1 5 " = " }{XPPEDIT 18 0 "x^3 /3-x-10/3" ",(*&%\"xG\"\"$\"\"$!\"\"\"\"\"F$F'*&\"#5F(\"\"$F'F'" } {TEXT -1 25 "\n I calcoli con Maple: " }}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 144 "int(t^2-1,t = 2 .. x);\nint(t^2-1,t = 2 .. 1)+int(-( t^2-1),t = 1 .. x);\nint(t^2-1,t = 2 .. 1)+int(-(t^2-1),t = 1 .. -1)+i nt((t^2-1),t = -1 .. x);" }}}{PARA 0 "" 0 "" {TEXT -1 143 "Facciamo un controllo grafico; dovremmo ottenere una funzione continua e un grafi co con una simmetria centrale rispetto al pun to di ascissa 0:" }} {EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 88 "F := x -> piecewise(x>=1,1/3 *x^3-x-2/3,x<1 and x>=-1,-2-1/3*x^3+x,x<-1,-10/3+1/3*x^3-x);" }}} {EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 15 "plot (F,-3..3);" }}}{PARA 0 "" 0 "" {TEXT -1 5 "OK\n\n(" }{TEXT 265 1 "b" }{TEXT -1 78 ") Facilmen te fattibile con la sostituzione t = 3u, u=t/3, t^2 = 9u, dt = 3 du" }}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 111 "Int(1/(t^2+9),t=0..x) = 1 /3*Int(1/(u^2+1),u=0..x/3);\n1/3*Int(1/(u^2+1),u=0..x/3) = 1/3*int(1/( u^2+1),u=0..x/3);" }}}{PARA 0 "" 0 "" {TEXT -1 20 "Controllo con Maple :" }}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 46 "Int(1/(t^2+9),t=0..x) = int(1/(t^2+9),t=0..x);" }}}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 0 " " }}}{PARA 0 "" 0 "" {TEXT 264 1 "\n" }}{PARA 0 "" 0 "" {TEXT -1 0 "" }}{PARA 0 "" 0 "" {TEXT -1 0 "" }}}{MARK "30 0" 0 }{VIEWOPTS 1 1 0 1 1 1803 }