[size=150][size=100]Prova a muovere x [i]intorno[/i] a 6 (anche variando il raggio dell'intorno). [br]Man mano che x si avvicina a 6, a quale valore si avvicina la sua immagine f(x)?[br]E quando x si avvicina a 2[/size]?[/size]

Diremo che:[br][center][img width=105,height=34]data:image/png;base64,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[/img][/center]quando [i][color=#ff0000]man mano che x si avvicina a x[sub]0[/sub] f(x) si avvicina a un certo valore l.[/color][/i]

Assegnata una funzione[br][center][size=150][i]f[/i]: D → R[/size][/center]con [math]D\subseteq R[/math]e x[sub]0[/sub] punto di accumulazione per D, per verificare che[br][br][center] [img width=105,height=34]data:image/png;base64,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[/img][/center]dovremo dimostrare che:[br][br][color=#cc0000]per ogni intorno di [i]l[/i] esiste un intorno di x[sub]0[/sub] tale per ogni x appartenente all'intorno di x[sub]0 [/sub]e al dominio, ad eccezione al più di x[sub]0[/sub], si ha che f(x) appartiene all'intorno di [i]l.[/i][br][br][/color]In simboli:[center][img]data:image/png;base64,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[/img][br][/center][u]ATTENZIONE[/u]: l'operazione di limite studia il comportamento della funzione [b]nell'intorno di x[/b][sub]0[/sub],[b] non in x[/b][sub]0[/sub], in tale punto la funzione potrebbe anche non esistere, mentre è indispensabile che x[sub]0[/sub] sia un punto di accumulazione per il dominio.[br]