函数与导数解答题之数列型不等式证明
例1.已知函数()()ln 3f x a x ax a R =--∈
(1)讨论函数)(x f 的单调性;
(2)证明:*1111ln(1)()23n n N n
+
+++>+∈L (3)证明:()*ln 2ln 3ln 4ln 5ln 12,2345n n n N n n ???<≥∈L (4)证明:()*22222ln 2ln 3ln 4ln 5ln 112,23452n n n n n N n n +?????≥∈ ???
L (5)证明:()444442
*44444ln 2ln 3ln 4ln 5ln (1)2,23454n n n n N n n
+???<≥∈L (6)求证:()()()
()222222121ln 2ln 3ln ...2,2321n n n n n N n n *-++++<≥∈+ (7)求证:()22221111111...12482n e n N *????????+
+++<∈ ????? ?????????
例2.已知函数2()ln(1)f x a x ax x =+--.
(1)若1x =为函数()f x 的零点,求a 的值;
(2)求()f x 的极值;
(3)证明:对任意正整数n ,2
22134232)1ln(n n n +++++
<+Λ.
例3.已知函数()x
f x e ax a =--(其中,a R e ∈是自然对数的底数, 2.71828e =…). (1)当a e =时,求函数()f x 的极值;(II )当01a ≤≤时,求证()0f x ≥;
(2)求证:对任意正整数n ,都有2111111222n e ??????+
+???+< ??? ???????
.
例4.设函数()ln 1f x x px =-+
(1)求函数()f x 的极值点;
(2)当p >0时,若对任意的x >0,恒有0)(≤x f ,求p 的取值范围; (3)证明:).2,()1(212ln 33ln 22ln 2222222≥∈+--<+++n N n n n n n
n Λ
例5.已知函数()ln 1f x x x =-+?
(1)求()f x 的最大值;
(2)证明不等式:()*121
n n n n e n N n n n e ??????+++<∈ ? ? ?-??????L