
Understanding Logarithms, Inverses, and L'Hopital's Rule
Explore the concepts of logarithms with base a, their inverses, common logarithms, and how to apply L'Hopital's Rule to evaluate limits. Discover examples and explanations for solving logarithmic equations and dealing with indeterminate forms in calculus.
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Presentation Transcript
Logarithms with base a For any positive number ? 1, ????? is the inverse function of ?? When ? = ? , we have ????? = (??????? ?? ??) = ln? The function ???10? is sometimes written simply as log? and is called the common logarithm of x ??????= ? ??????= ? ? > 0 ??? ? ? = ?? ? =ln? ??? ? = ????? ln? = ?ln? ln? ????? =ln? ln? ? ?? ? ?? ln? ln? ln?.1 1 ?.?? ????? = = ??
Example: ? ?????10(3? + 1) ? ?? ln(3? + 1) ln10 1 1 3 = = ln10. (3? + 1).3 = ln 10 .(3? + 1) ???2? ? ?? Example: ln? ln2 ? ln2 ln? 1 = ?? = ?? ? ?? =?? ? = ln? ?2 2+ ? ? 1 1 = ln2 ??? = ln2 ???2 2 ???2 2ln2+ ? 1 = ln2. + ? = ?? ??= ?? Example:????? ? ? ???????????? ???????? ?? ?= ??? ? = ???+?= ???.?? ln? = ?? + ? ? = ? ???
???????: ????? ?3?4+ 5 = 2716 ?3? 4= 2711 ???3? 4= ln(2711) 3? 4 = ln(2711) 3? = ln 2711 + 4 ? =ln 2711 + 4 3 ???????: ????? 10?= 41 log10?= log41 ? = log41 = 3.968 ???????: ????? ?4?+ ?2? 6 = 0 ?2?+ 3 ?2? 2 = 0 ?2?+ 3 = 0 ?? ?2? 2 = 0 ?2?= 3 ?? ???????? ? =ln2 2 ?2?= 2 2? = ln2 = 0.347
?? ??= 1 + ? ?? , ? > 1 Example: ????? ? ? ???????????? ???????? ?? 1 + ?= ???? ln 1 + ? = ??+ ? ?? ??= ?(?2+ 1) Example: Solve the equation ? ? + 1 ? ? + 1 ?? = ? ?2+ 1 ?? ??? ?2+ 1= ??? ? + 1 ? 1 ? + 1= 1 ? + 1 ??? ?2+ 1= 1 1 ?? ? + 1 1 2ln 1 + ?2= ? ?? ? + 1 + ? ???????:????? log? + log3 = 2log4 log2 log3? = log16 log2 ???3? = ???16 2 ? =8 3? = 8 3
Indeterminate forms and Hopitals Rule Using Hopital s Rule to find the limits of some sequences Theorem ?? lim ? ? ? (?) ? (?) ?(?) ?(?)=0 ? ?? lim ?(?) ?(?)= lim 0 ?? ? ? ? ? sin2? ? ???????: ???? lim ? 0 0 0 ,??? ??????? ? ???? 2cos? 1 ?2+ ? 1 2?2+ 5 2? + 1 4? = = lim ? 0 = 2 ???????: ???? lim ? ??? ??????? ? ???? = ,??? ??????? ? ???? ?????? ???? = lim ? 2 4=1 = lim ? 2
? tan? sin? ? ???????: ???? lim ? 0 = 0 ,??? ??????? ? ???? 0 0 1 ???2? cos? 1 ??? ??????? ? ???? ?????? ???? 2sec?.sec????? sin? 1 ???2? ? 0 = lim ? 0 0 ? 0 ???2?tan? 1 ???3?= 2 = lim ? 0 = 2 lim sin? 1 = 2 lim cos?= 2 lim ? 0 ? Indeterminate form ? ? ?? ???????: ???? lim ? 0?ln? ln? 1 ? ,??? ??????? ? ???? = 0. ?? lim ? 0 1 ? lim ? 0 = lim ? 0 ? = 0 1 ?2
???????:???? lim 1 tan? sec2? ? ? 1 tan? 1 sec2? 4 1 tan? cos2? =0 0 ,??? ??????? ? ???? = 0. ?? lim = lim ? ? ? ? 4 4 1 ???2? 2sin2?= lim ???2? 2sin2?=2 = lim ? ? 2= 1 ? ? 4 4 ? Indeterminate form ? ?? 1 ? 1 ???????:???? lim ???? ? 0 ??? ? ? ???? ?=? ? ??? ??????? ? ???? = ?? = lim ? ? cos? 1 ???? ? + ????= 0 0 ,??? ??????? ? ???? ?????? ???? sin? ???? ? + cos? + cos?=0 = lim ? 0 = lim ? 0 2= 0
?2+ ? ? ???????:???? lim ? ?2+ ? + ? ?2+ ? ? . = ?? lim ?2+ ? + ? ? ?2+ ? ?2 ? = ??? ??????? ? ???? lim ? = lim ? , ?2+ ? + ? ?2+ ? + ? 1 = lim ? 1 1 2?2+ ? 1 2 2? + 1 + 1 1 =1 = lim ? = lim ? 2 +1 2? + 1 2? 1 +1 2 + 1 ? + 1 2 1 +1 ? ? ??? ???? ??, ? ,? 1 ? ???????: ???? lim ? 01 + ? 1 ? = 1 ? = 1 + ? ln? =1 ?ln 1 + ?
1 ?ln 1 + ? ??? ??????? ? ???? lim ? 0ln? = lim ln(1 + ?) ? ? 0 =0 = lim ? 0 0 , 1 1 + ? 1 = lim ? 0 lim ? 0ln? = 1 lim = 1 ? 0????= ? lim ? 0? = ? 1 ?= ? lim ? 01 + ? 1 ? ? 0??+ ? ???????: ???? lim = 1 ln? =1 ln(??+ ?) 1 ? ? = ??+ ? ?(??+ ?) =0 0 lim ? 0ln? = lim ? ? 0 1 ??+ ???+ 1 1 2 1 1= 2 lim ? 0ln? = lim = ? 0
lim ? 0ln? = 2 ? 0?ln ?= ?2 lim ? = ?2 1 ?= ?2 ? 0??+ ? lim