ữỡ
ợ ừ số
Pữỡ t ỡ
ỵ tt é ú t sỷ ử ỵ s t ợ ừ ởt số õ
ỵ số {a } ỡ t tr t tỗ t ợ lim
n
an
n+
ỳ
ỡ
lim an = supan .
n+
nN
số {an } ỡ ữợ t tỗ t ợ n+
lim an ỡ ỳ
lim an = inf an .
n+
nN
ử
ử số {u } ữủ ữ s
n
u1 = 1
un+1 = un +
ợ
lim
n+
u2n
1999 .
u2
un
u1
+
+ ããã +
.
u2
u3
un+1
ứ tt t õ
ứ õ s r
un
u2n
1999(un+1 un )
=
=
= 1999
un+1
un+1 un
un+1 un
1
1
un
un+1
u1
u2
uk
+
+ ããã +
= 1999
u2
u3
uk+1
.
1
1
u1
uk+1
.
t {un } ỡ t ỡ ỳ un 1, n {un } tr
õ t ỵ ở tử ỡ tỗ t ợ n+
lim un = L. ứ ổ tự tr ỗ
L
ừ q ợ n t ữủ L = L + 1999
L = 0 ổ ỵ
un 1. {un } ổ tr õ n+
lim un = +.
k tr ú ỵ tr t ữủ
2
lim
k+
u1
u2
uk
+
+ ããã +
u2
u3
uk+1
= lim 1999
k+
1
1
u1
uk+1
= 1999 lim
ởt số t ử
số {u } ữủ ữ s
n
u1 = 2
un+1 =
u2n +1999un
,
2000
{Sn } ợ
n
Sn =
k=1
ợ
n N.
uk
.
uk+1 1
lim Sn .
n+
số {u } ữủ ữ s
n
u1 N
un+1 =
1
2
ln 1 + u2n ,
n N.
ự r số {xn } ở tử
số {xn} ữủ ữ s
0 < xn < 1
xn+1 (1 xn ) 1 ,
4
ự r
lim xn =
n+
n N.
1
.
2
f : [0, ) [0, ) tử sỷ r
f () = ,
f () = ,
, 0,
õ t = = a.
ự r {xn+1 = f (xn )} ợ x0 > 0 ở tử a.
1
k+ uk+1
= 1999.
✸
❇➔✐ ✺✳ ❈❤♦ ❞➣② sè {a } ✤÷ñ❝ ①→❝ ✤à♥❤ ♥❤÷ s❛✉✿
n
an =
1
2
an−1 +
2015
an−1
,
n ≥ 2,
a1 = 2016.
√
lim an = 2015.
❈❤ù♥❣ ♠✐♥❤ r➡♥❣ n→+∞
❇➔✐ ✻✳ ●✐↔ sû r➡♥❣ ❞➣② {an} ❜à ❝❤➦♥ ✈➔ t❤ä❛ ♠➣♥
an+2 ≤
1
2
an+1 + an
3
3
✈î✐ n ≥ 1.
❈❤ù♥❣ ♠✐♥❤ r➡♥❣ ❞➣② tr➯♥ ❤ë✐ tö✳
✶✳✷ ◆❣✉②➯♥ ❧þ ❦➭♣
▲þ t❤✉②➳t✳ ✣è✐ ✈î✐ ❞↕♥❣ ❜➔✐ t➟♣ ♥➔② t❛ sû ❞ö♥❣ ✤à♥❤ ❧þ ❞÷î✐ ✤➙② ✤➸ ❧➔♠ ❜➔✐ t➟♣✳
✣à♥❤ ❧þ ✶✳✸✳ ❈❤♦ ❜❛ ❞➣② sè {a , b , c } t❤ä❛ ♠➣♥ a ≤ b ≤ c . ●✐↔ sû r➡♥❣
n
lim cn = A.
n→+∞
n
n
n
n
n
❑❤✐ ✤â t❛ ❝â n→+∞
lim bn = A.
lim an =
n→+∞
✣è✐ ✈î✐ ❜➔✐ t➟♣ ②➯✉ ❝➛✉ t➼♥❤ ❣✐î✐ ❤↕♥ ❝õ❛ ♠ët ❞➣② n→+∞
lim bn ♥➔♦ ✤â✱ t❛ ❝â t❤➸ t➻♠ ❝→❝ ❞➣② an , cn
s❛♦ ❝❤♦ an ≤ bn ≤ cn ✈î✐ n ✤õ ❧î♥✱ ✈➔ ❤ì♥ ♥ú❛ ❝→❝ ❣✐î✐ ❤↕♥ n→+∞
lim an , lim cn ♣❤↔✐ ❞➵ t➼♥❤✱ ✈➔
n→+∞
♣❤↔✐ ❜➡♥❣ ♥❤❛✉✳ ❑❤✐ ✤â →♣ ❞ö♥❣ ✤à♥❤ ❧þ tr➯♥ t❛ s✉② r❛ ✤÷ñ❝ ❣✐î✐ ❤↕♥ ❝õ❛ ❞➣② n→+∞
lim bn .
❇➯♥ ❝↕♥❤ ✤â✱ ❝❤ó♥❣ t❛ ❝ô♥❣ ❝➛♥ tî✐ ♠ët sè ❜➜t ✤➥♥❣ t❤ù❝ s❛✉✳
❱î✐ x > 0 t❛ ❝â
✭❛✮
1−
x2
x4
x2
< cos x < 1 −
+ .
2
2
4!
x−
x3
x3
x5
< sin x < x −
+ .
3!
3!
5!
✭❜✮
✭❝✮
✭❞✮
√
1
1
1
1
1
1 + x − x2 < 1 + x < 1 + x − x2 + x3 .
2
8
2
8
16
x−
⑩♣ ❞ö♥❣✳
x2
x3
x4
x2
x3
+
−
< ln(1 + x) < x −
+ .
2
3
4
2
3
❱➼ ❞ö ✶✳✹✳ ❈❤♦ ❜✐➳t r➡♥❣
n
Sn =
❈❤ù♥❣ ♠✐♥❤ r➡♥❣
( 1+
k=1
k
− 1).
n2
lim Sn =
n→+∞
1
.
4
✹
❈❤ù♥❣ ♠✐♥❤✳ ❚r÷î❝ t✐➯♥✱ t❛ ❝❤ó þ r➡♥❣ ✈î✐ x > −1, t❛ ❝â ❜➜t ✤➥♥❣ t❤ù❝ s❛✉
√
x
x
< 1+x−1< .
2+x
2
⑩♣ ❞ö♥❣ ❜➜t ✤➥♥❣ t❤ù❝ tr➯♥✱ t❤❛② x ❧➛♥ ❧÷ñt ❜ð✐ nk , ❝❤ó♥❣ t❛ ♥❤➟♥ ✤÷ñ❝
2
k
<
2n2 + k
1+
k
k
− 1 < 2.
n2
2n
▲➜② tê♥❣ ❝õ❛ ❜➜t ✤➥♥❣ t❤ù❝ tr➯♥ t❤❡♦ k tø 1 ✤➳♥ n t❛ ♥❤➟♥ ✤÷ñ❝
n
k=1
❚❛ ❝â
n
k=1
k
1
= 2
2n2
2n
k
< Sn <
2
2n + k
n
n
k=1
❦❤✐ n → ∞.
1
n(n + 1)
→
4n2
4
k=
k=1
✭✶✳✷✮
k
.
2n2
✭✶✳✸✮
▼➦t ❦❤→❝✱ t❛ ❧↕✐ ❝â
lim {
n→+∞
▲↕✐ ❝â
n
k=1
1
2n2
n
n
k−
k=1
k2
<
2
2n (2n2 + k)
k=1
n
k=1
❉♦ ✤â
lim {
n→+∞
k
} = lim
n→+∞
2n2 + k
n
k=1
k2
2n2 (2n2
k2
n(n + 1)(2n + 1)
=
→0
4
4n
24n4
1
2n2
n
n
k−
k=1
❈❤ó þ ✭✶✳✸✮ t❛ ♥❤➟♥ ✤÷ñ❝
k=1
n
lim
n→+∞
k=1
+ k)
.
❦❤✐ n → ∞.
k
} = 0,
+k
2n2
k
1
= .
2
2n
4
✭✶✳✹✮
▲➜② ❣✐î✐ ❤↕♥ tr♦♥❣ ✭✶✳✷✮ ❦❤✐ n → ∞ ✈➔ ❝❤ó þ ✭✶✳✸✮ ✈➔ ✭✶✳✹✮ t❤❡♦ ♥❣✉②➯♥ ❧þ ❦➭♣ t❛ ♥❤➟♥ ✤÷ñ❝
lim Sn =
n→+∞
1
.
4
▼ët sè ❜➔✐ t➟♣ →♣ ❞ö♥❣✳
❇➔✐ ✶✳ ❈❤♦ ❞➣② sè {x } ✤÷ñ❝ ①→❝ ✤à♥❤ ❜ð✐
n
xn = (1 +
❚➻♠ n→+∞
lim lnxn .
1
2
n
)(1 + 2 ) · · · (1 + 2 ).
2
n
n
n
t sỹ ở tử ừ số s
xn =
n2
n2
n2
+
+ ããã +
.
6
6
n +1
n +2
n6 + n
t sỹ ở tử ừ số s
xn =
[] + [2] + ã ã ã + [n]
,
n2
tr õ [x] số ợ t ổ ữủt q x, ởt số tỹ t
ợ s
n
lim
n+
lim
(
lim
n+
{a } {b }
n
1+
k=1
n
k2
1).
n3
12 + 22 + ã ã ã + n2 .
n+
3
1
2
n
+
+ ããã + 2
.
n2 + 1 n2 + 2
n +n
n
a1 = 3, b1 = 2, an+1 = an + 2bn
ỡ ỳ
bn+1 = an + bn .
an
, n N.
bn
|cn+1 2| < 21 |cn 2|, n N.
cn =
ự r
n+
lim cn .
ợ
ln2 n
n+ n
n2
lim
k=2
1
.
ln k ln (N k)
số tờ qt
ỵ tt ố ợ t tổ tữớ s t ợ ừ ởt số
lim an
n
tr õ {an } ữủ ữợ tr ỗ
t t sỷ ử ữỡ s t số tờ qt ừ
số tự ữ số {an } af (n) s õ sỷ ử tự ồ t ợ
lim f (n).
n
ử
ử (0, 2). ợ
ừ số {xn } ữủ
lim xn
n+
xn+1 = xn + (1 )xn1
t , x0 , x1 .
tt t õ xn xn1
n1
xn xn1 = ( 1)
n = 1, 2, ã ã ã
= ( 1)(xn1 xn2 ).
(x1 x0 ).
õ
n
xn x0 =
q t ự ữủ
n
( 1)k1
(xk xk1 ) = (x1 x0 )
k=1
k=1
(0, 2) | 1| < 1. t t õ
n
( 1)k1 =
k=1
1 ( 1)n
1 ( 1)n
=
.
1 ( 1)
2
ợ n tr ú ỵ tự tr t ữủ
lim xn = x0 + lim (x1 x0 )
n+
n+
1 ( 1)n
(1 )x0 + x1
=
.
2
2
ởt số t ử
ữủ ữ s f
1
ự r ợ
lim
n+
= 1, f2 = 2, fn+1 = fn + fn1 ,
fn+1
fn
, n 2.
tỗ t ợ tr
x0 = a, x1 = b xn+2 = 13 (xn + 2xn+1), n N. ự r ợ n+
lim xn
tỗ t ợ õ
ọ tữỡ tỹ tr
x0 = a, x1 = b, xn = (1
sỷ r b R, a
n
aR
xn+1 = an + bxn . ự r
xn
xn
1
1
)xn1 + xn2 , n N.
n
n
a
1b
a
1b
|b| < 1;
|b| > 1 x1 +
ak
= 0.
bk
✼
✶✳✹ P❤÷ì♥❣ ♣❤→♣ t➼❝❤ ♣❤➙♥
▲þ t❤✉②➳t✳
⑩♣ ❞ö♥❣✳
❱➼ ❞ö ✶✳✻✳ ❚➼♥❤ ❣✐î✐ ❤↕♥
1
1
1
+
+ ··· +
.
n+1 n+2
3n
lim
n→+∞
❚❛ ❝â
Sn :=
❳➨t ❤➔♠ sè f (x) =
✤♦↕♥ ♥➔②✳ ❉♦ ✤â
1
1
2 +x
1
1
1
1
+
+ ··· +
=
n+1 n+2
3n
2n
1
k=1 2
1
.
k
+ 2n
tr➯♥ ✤♦↕♥ [0, 1]. ❍➔♠ f ❧➔ ❤➔♠ ❧✐➯♥ tö❝ tr➯♥ [0, 1] ♥➯♥ ❦❤↔ t➼❝❤ tr➯♥
1
1
n→+∞ 2n
2n
f(
f (x)dx = lim
0
▲↕✐ ❝â
2n
1
k=1
1
k
) = lim
n→+∞ 2n
2n
2n
1
k=1 2
1
.
k
+ 2n
1
f (x)dx =
0
1
2
0
❉♦ ✤â✱ t❛ ❝â
1
3
1
1
dx = ln ( + x)|10 = ln − ln = ln 3.
2
2
2
+x
1
1
1
+
+ ··· +
n+1 n+2
3n
lim
n→+∞
= ln 3.
▼ët sè ❜➔✐ t➟♣ →♣ ❞ö♥❣✳
❇➔✐ ✶✳ ❚➼♥❤ ❝→❝ ❣✐î✐ ❤↕♥ s❛✉✳
✐✳
lim n2
n→+∞
n3
✐✐✳
lim
n→+∞
✐✐✐✳
1
1
1
+ 3
+ ··· + 3
.
3
3
+1
n +2
n + n3
1 k + 2 k + · · · + nk
,
nk+1
1
n→+∞ n
(n + 1)(n + 2) · · · (n + n).
lim
✐✈✳
lim
n→+∞
sin
k ≥ 0.
n
n
n
.
+ sin 2
+ · · · + sin 2
n2 + 1 2
n + 22
n + n2
✈✳
1
lim
n→+∞
2
n
2n
2n
2n
+
+ ··· +
1
n+1 n+ 2
n + n1
.
ự r ợ
sin n+1
lim
1
n+
+
2
sin n+1
+ ããã +
2
n
sin n+1
n
ởt số ữỡ
ự r f tử tr [0, 1] t
lim n
n+
1
n
i
f( )
n
i=1
f (x)dx =
f (1) f (0)
.
2
0
ỷ ử t q tr t
lim n
n+
1k + 2k + ã ã ã + nk
1
,
nk+1
k+1
ợ k 0, t
lim
n+
k 0.
1k + 3k + ã ã ã + (2n 1)k
.
nk+1
Pữỡ ợ tr ữợ
ỵ tt r ố ự ợ
ừ ởt số tỗ t ổ t ự
ợ tr ừ số õ ợ ữợ ừ số õ ổ tự t
tr õ tự s ổ
lim an
n+
lim inf an = lim sup an .
n
n
ử
ử sỷ r {a } ởt số tỹ s
n
tỹ k số ữỡ s
lim an = 1
n+
{bn } số
lim (bn an bn+k ) = l,
n+
ự r l = 0.
ự t
b = lim inf bn ,
n
B = lim sup bn .
n
{bn } số b, B số ỳ ừ lim inf n an , lim supn an
tỗ t {bp }, {bq } ừ {bn } s bp b, bq B r . an 1
bn an bn+k l n {bp +k }, {bq +k } ừ {bn } tữỡ ự t tợ b l
B l r . q b l l B l l. õ l = 0.
r
r
r
r
r
r
✾
▼ët sè ❜➔✐ t➟♣ →♣ ❞ö♥❣✳
❇➔✐ ✶✳ ❈❤♦ ❞➣② sè t❤ü❝ {a } s❛♦ ❝❤♦ a
n
n
≥ 1,
∀n ≥ 1
✈➔ ❞➣② {an + a−1
n } ❤ë✐ tö✳ ❈❤ù♥❣ ♠✐♥❤
r➡♥❣ ❞➣② {an } ❤ë✐ tö✳
❇➔✐ ✷✳ ❈❤♦ ❞➣② sè t❤ü❝ {an} s❛♦ ❝❤♦ n→+∞
lim (2an+1 − an ) = l. ❈❤ù♥❣ ♠✐♥❤ r➡♥❣ lim an = l.
n→+∞
❇➔✐ ✸✳ ❈❤♦ ❞➣② sè ❞÷ì♥❣ {an} s❛♦ ❝❤♦ n→+∞
lim an = L. ❈❤ù♥❣ ♠✐♥❤ r➡♥❣
1
lim (a1 a2 · · · an ) n = L.
n→+∞
❈❤÷ì♥❣ ✷
❚➼❝❤ ♣❤➙♥
✷✳✶ ❚➼♥❤ t➼❝❤ ♣❤➙♥
✣è✐ ✈î✐ ❞↕♥❣ ❜➔✐ t➟♣ ♥➔② t❤➻ ❝❤õ ②➳✉ ❧➔ ❞ò ♣❤➨♣ ✤ê✐ ❜✐➳♥ ✈➔ t➼❝❤ ♣❤➙♥ ✤➸ ✤÷❛ t➼❝❤ ♣❤➙♥ ❜❛♥ ✤➛✉
✈➲ t➼❝❤ ♣❤➙♥ ❞➵ t➼♥❤ ❤ì♥✳ ❇➯♥ ❝↕♥❤ ✤â ♠ët sè ❜➔✐ t➟♣ s➩ →♣ ❞ö♥❣ ❝→❝ ❦➳t q✉↔ s❛✉ ✤➸ t➼♥❤ t➼❝❤ ♣❤➙♥✳
▼➺♥❤ ✤➲ ✷✳✶✳ ❈❤♦ f : [−a, a] → R ❧➔ ❤➔♠ ❧✐➯♥ tö❝ ✈➔ ❝❤➤♥ ✭a > 0.✮ ❈❤ù♥❣ ♠✐♥❤ r➡♥❣
a
a
f (x)
dx =
1 + ex
−a
✭✷✳✶✮
f (x)dx
0
▼➺♥❤ ✤➲ ✷✳✷✳ ❈❤♦ f : [−a, a] → R ❧➔ ❤➔♠ ❧✐➯♥ tö❝ ✭a > 0.✮ ❈❤ù♥❣ ♠✐♥❤ r➡♥❣
✶✳
a
a
f (x)dx = 2
−a
✷✳
♥➳✉ f ❧➔ ❤➔♠ ❝❤➤♥ .
f (x)dx
✭✷✳✷✮
0
a
f (x)dx = 0
♥➳✉ f ❧➔ ❤➔♠ ❧➫ .
✭✷✳✸✮
−a
▼➺♥❤ ✤➲ ✷✳✸✳ ❈❤♦ ❤➔♠ f : R → R ❧➔ ❤➔♠ ❧✐➯♥ tö❝ ✈➔ t✉➛♥ ❤♦➔♥ ❝❤✉ ❦➻ T > 0. ❈❤ù♥❣ ♠✐♥❤
r➡♥❣
✶✳ ✈î✐ ♠é✐ sè t❤ü❝ a t❛ ❝â
a+T
T
f (x)dx =
a
f (x)dx,
✭✷✳✹✮
0
✷✳ ✈î✐ ♠é✐ sè t❤ü❝ a < b t❛ ❝â
b
lim
n→+∞
b−a
f (nx)dx =
T
a
T
f (x)dx.
0
✶✵
✭✷✳✺✮
f : [0, 1] R tử ự r
xf (sin x)dx =
2
0
f (sin x)dx.
0
ử t
2
I1 =
2
cos2014 (x)
dx.
1x+ x2 +1
ự ố ợ t ú t s ũ ờ t t st
ữợ t t t số õ ủ õ trữợ t t tỷ
ủ ú t ữủ õ
1x+
1
(1 x) + x2 + 1
(1 x) + x2 + 1
=
=
.
2x
x2 + 1
((1 x) + x2 + 1)(1 x + x2 + 1)
t t tự t s õ ũ t tứ t
õ õ tự tr ỏ ự õ tự
t ữủ t tr t ỷ ữủ số t
ữ ữợ t xn cos2014 (x) tr õ n ởt số ữỡ õ
tỷ t s t f (x) = 1x+1 x +1 t tỷ
1
= f (x).
f (x) = x + x2 + 1. õ t q st t f (x) = x+1x +1 =
(x)+ (x) +1
õ t ủ ỵ ú t õ tr ữ t t
t ỡ é t q st t f (x) õ ủ ỵ t ờ
t = x. ợ ờ t s ữủ t q
2
2
2
2
2014
cos
(x)
dx =
1 + f (x)
I1 =
2
2
2
=
2
2
=
2
cos2014 (t)
dt
1 + t + t2 + 1
cos2014 (t)
dt
1 + t + t2 + 1
f (x) cos2014 (x)
dx.
1 + f (x)
2
ứ õ s r
2
2I1 =
2
cos2014 (x)
dx +
1 + f (x)
2
2
f (x) cos2014 (x)
dx =
1 + f (x)
2
cos2014 (x)dx.
2
ợ sỷ ử ổ tự tr ỗ t tứ t t õ t t
ữủ t I1 . ỏ ồ
✶✷
✷✳
π
2014
I2 =
0
π
2
✸✳
I3 =
✹✳
I4 =
0
1
0
1
1+ecos 2014x dx.
ex sin x
(cos x+sin x)2 dx.
x2014
2
2014
1+x+ x2 +···+ x2014!
dx.
✷✳✷ ❇➜t ✤➥♥❣ t❤ù❝ t➼❝❤ ♣❤➙♥
✣à♥❤ ❧þ ✷✳✻✳ ❈❤♦ f, g ❧➔ ❝→❝ ❤➔♠ ①→❝ ✤à♥❤ ✈➔ ❦❤↔ t➼❝❤ tr➯♥ ✤♦↕♥ [a, b] s❛♦ ❝❤♦ f ≥ g. ❑❤✐ ✤â t❛ ❝â
b
b
f (x)dx ≥
f (x)dx.
a
a
✣à♥❤ ❧þ ✷✳✼ ✭❇➜t ✤➥♥❣ t❤ù❝ ❈❛✉❝❤② ✲ ❙❝❤✇❛r③✮✳ ❈❤♦ f, g ❧➔ ❝→❝ ❤➔♠ ①→❝ ✤à♥❤ ✈➔ ❦❤↔ t➼❝❤ tr➯♥
✤♦↕♥ [a, b]. ❑❤✐ ✤â t❛ ❝â
2
b
b
a
b
2
f (x)g(x)dx ≤
g 2 (x)dx.
f (x)dx
a
a
❈❤ù♥❣ ♠✐♥❤✳ ❚❛ ❝â✱ ✈î✐ ♠å✐ x ∈ R t❤➻
b
b
2
0≤
(xf (t) + g(t)) dt =x
a
2
b
b
2
(f (t)) dt + 2x
a
g 2 (t)dt
f (t)g(t)dt +
a
a
=Ax2 + Bx + C,
tr♦♥❣ ✤â
b
b
2
A=
(f (t)) dt,
B=
a
❚❛♠ t❤ù❝ ❜➟❝ ❤❛✐✱ Ax
2
b
f (t)g(t)dt,
a
+ Bx + C
a
❦❤æ♥❣ ➙♠ ✈î✐ ♠å✐ x ∈ R ❦❤✐ ✈➔ ❝❤➾ ❦❤✐ B 2 − AC ≤ 0, tù❝ ❧➔
2
b
b
a
b
2
f (t)g(t)dt ≤
g 2 (t)dt.
(f (t)) dt
a
✣➥♥❣ t❤ù❝ ①↔② r❛ ❦❤✐ ✈➔ ❝❤➾ ❦❤✐
a
b
2
(xf (t) + g(t)) dt = 0
❤❛②
g 2 (t)dt.
C=
a
xf (t) = g(t),
t ∈ [a, b].
✶✸
❱➼ ❞ö ✷✳✽✳ ❈❤ù♥❣ ♠✐♥❤ r➡♥❣ ♥➳✉ f ❧➔ ❝→❝ ❤➔♠ ①→❝ ✤à♥❤ ✈➔ ❦❤↔ t➼❝❤ tr➯♥ ✤♦↕♥ [a, b], t❤➻
2
b
a
b
f 2 (x)dx.
f (x) cos xdx ≤ (b − a)
f (x) sin xdx +
2
b
a
a
❈❤ù♥❣ ♠✐♥❤✳ ⑩♣ ❞ö♥❣ ✣à♥❤ ❧þ ✷✳✼ ✈î✐ g(x) = sin x ✈➔ g(x) = cos x t❛ ♥❤➟♥ ✤÷ñ❝
2
b
b
a
2
b
a
b
a
b
2
f (x) cos xdx ≤
sin2 (x)dx
f (x)dx
a
✈➔
b
2
f (x) sin xdx ≤
cos2 (x)dx.
f (x)dx
a
a
❉♦ ✤â
b
2
a
b
a
b
f (x)dx
a
b
2
2
f (x) cos xdx ≤
f (x) sin xdx +
2
b
sin (x)dx +
a
a
sin2 (x)dx +
a
a
(sin2 x + cos2 x)dx
a
b
b
2
=
cos2 (x)dx
b
f 2 (x)dx
=
b
a
b
a
b
f 2 (x)dx
=
cos2 (x)dx
f (x)dx
a
b
b
2
f (x)dx
a
dx
a
b
f 2 (x)dx.
=(b − a)
a
❱➼ ❞ö ✷✳✾✳ ●✐↔ sû r➡♥❣ f : [a, b] → [m, M ] ✈➔
b
f (x)dx = 0.
a
❈❤ù♥❣ ♠✐♥❤ r➡♥❣
b
f 2 (x)dx ≤ −mM (b − a).
✭✷✳✼✮
a
P❤➙♥ t➼❝❤✿ Ð ✤➙② t❛ ❝è ❣➢♥❣ →♣ ❞ö♥❣ ♠ët tr♦♥❣ ❤❛✐ ✤à♥❤ ❧þ✿ ✣à♥❤ ❧þ ✷✳✻ ❤♦➦❝ ✣à♥❤ ❧þ ✷✳✼ ✤➸ ❝❤ù♥❣
♠✐♥❤ ❜➔✐ t♦→♥ tr➯♥✳ ◆➳✉ t❛ →♣ ❞ö♥❣ ✣à♥❤ ❧þ ✷✳✼ ✤➸ ❝❤ù♥❣ ♠✐♥❤✱ ❦❤✐ ✤â t❛ ❝❤÷❛ t❤➜② ①✉➜t ❤✐➺♥ ❤➔♠ g,
tr♦♥❣ tr÷í♥❣ ❤ñ♣ ♥➔② ♠✉è♥ ①✉➜t ❤✐➺♥ ❤➔♠ g t❛ ❝â t❤➸ ♣❤➙♥ t➼❝❤ f t❤➔♥❤ t➼❝❤ ❝õ❛ ❤❛✐ ❤➔♠ ♥➔♦ ✤â✳ ✣➸
❝â ♣❤➙♥ t➼❝❤ f t❤➔♥❤ t➼❝❤ ❝õ❛ ❤❛✐ ❤➔♠ t❤➻ f ❝❤➾ ❝â t❤➸ ❝â ♣❤➙♥ t➼❝❤ ❞↕♥❣ f = αf α, α = 0 ✭t↕✐ s❛♦
❄❄❄❄❄❄❄❄❄✮✳ ❑❤✐ ✤â t❛ ❝â
✶✹
2
b
0=
b
f (x)dx =
a
2
f (x)
αdx
α
a
b
b
f (x) 2
(
) dx
α
≤
a
α2 dx
a
b
=α2 (b − a)
(
f (x) 2
) dx
α
a
b
f 2 (x)dx.
=(b − a)
a
✣➳♥ ✤➙②✱ ❝❤ó♥❣ t❛ ❝❤➥♥❣ ❣✐↔✐ q✉②➳t ✤÷ñ❝ ✈➜♥ ✤➲ ❣➻✳
◆➳✉ ♥❤÷ t❛ ❦❤æ♥❣ ♣❤➙♥ t➼❝❤ f = αf × α ♠➔ t➻♠ ♠ët ♣❤➙♥ t➼❝❤ ❦❤→❝ ✈➔ →♣ ❞ö♥❣ ✣à♥❤ ❧þ ✷✳✼ ✤➸
❝❤ù♥❣ ♠✐♥❤ ✭✷✳✼✮ ♥â✐ ❝❤✉♥❣ ❧➔ r➜t ❦❤â✳
✣➳♥ ✤➙②✱ t❛ t❤û ♥❣❤➽ tî✐ ✈✐➺❝ →♣ ❞ö♥❣ ✣à♥❤ ❧þ ✷✳✻ ①❡♠ s❛♦✳ ✣➸ →♣ ❞ö♥❣ ✤à♥❤ ❧þ ♥➔②✱ t❛ ❝➛♥ t➻♠
❤➔♠ g(x) ≥ 0, ∀x ∈ [a, b]. ❚❛ ❝❤ó þ r➡♥❣ f : [a, b] → [m, M ]. ❉♦ ✤â✱ t❛ ❝â f (x) − m ≥ 0, M − f (x) ≥
0, ∀x ∈ [a, b]. ◆❤÷ ✈➟② ❤➔♠ g tr♦♥❣ tr÷í♥❣ ❤ñ♣ ♥➔② ❝â t❤➸ ❧➔ f (x) − m ❤♦➦❝ M − f (x) ❤♦➦❝ ♠ët ❜✐➸✉
t❤ù❝ ♥➔♦ ✤â ❝õ❛ ♠ët ❤♦➦❝ ❝↔ ❤❛✐ t❤ø❛ sè tr➯♥✳ ▼➦t ❦❤→❝✱ t❛ ❧↕✐ ❝❤ó þ tr♦♥❣ ✭✷✳✼✮ ❝â ①✉➜t ❤✐➺♥ ❝↔ m
✈➔ M, ❝❤♦ ♥➯♥ t❛ ❞ü ✤♦→♥ g ❝➛♥ ①✉➜t ❤✐➺♥ ❝↔ ❤❛✐ t❤ø❛ sè f (x) − m ✈➔ M − f (x). ◆❤÷ ✈➟② t❛ ❞ü ✤♦→♥
❤➔♠ g ❧➔ (f (x) − m)(M − f (x)). ❙❛✉ ✤â t❛ t❤û →♣ ❞ö♥❣ ✣à♥❤ ❧þ ✷✳✻✱ ✈➔ t❛ ❝â ❝❤ù♥❣ ♠✐♥❤ ♥❤÷ s❛✉✳
❈❤ù♥❣ ♠✐♥❤✳ ✣➦t g(x) = (f (x) − m)(M − f (x)),
→♣ ❞ö♥❣ ✣à♥❤ ❧þ ✷✳✻ t❛ ❝â
b
0≤
∀x ∈ [a, b].
❑❤✐ ✤â g(x) ≥ 0,
∀x ∈ [a, b].
b
(f (x) − m)(M − f (x))dx
g(x)dx =
a
a
b
−f 2 (x) + (n + M )f (x) − mM dx
=
a
b
b
f 2 (x)dx +
=−
a
b
a
b
f 2 (x)dx − mM (b − a).
=−
a
❉♦ ✤â✱ t❛ ❝â ✭✷✳✼✮✳
−mM dx
(n + M )f (x)dx +
a
❑❤✐ ✤â
✶✺
❱➼ ❞ö ✷✳✶✵✳ ❈❤ù♥❣ ♠✐♥❤ r➡♥❣✱ ♥➳✉ f ❧➔ ❝→❝ ❤➔♠ ①→❝ ✤à♥❤✱ ❞÷ì♥❣ ✈➔ ❦❤↔ t➼❝❤ tr➯♥ ✤♦↕♥ [a, b], t❤➻
b
b
2
(b − a) ≤
1
dx.
f (x)
f (x)dx
a
a
❍ì♥ ♥ú❛✱ ♥➳✉ 0 < m ≤ f (x) ≤ M, t❤➻
b
b
f (x)dx
1
(m + M )2
dx ≤
(b − a)2 .
f (x)
4mM
a
a
❱➼ ❞ö ✷✳✶✶✳ ❈❤♦ f ∈ C ([a, b]), f (a) = f (b) = 0 ✈➔
b
1
f 2 (x)dx = 1.
a
❈❤ù♥❣ ♠✐♥❤ r➡♥❣
b
xf (x)f (x)dx = −
1
2
✭✷✳✽✮
a
✈➔
b
1
≤
4
b
2
x2 f 2 (x)dx.
(f (x)) dx
a
a
❍÷î♥❣ ❞➝♥✿ ⑩♣ ❞ö♥❣ t➼❝❤ ♣❤➙♥ tø♥❣ ♣❤➛♥ ❝❤♦ ✈➳ tr→✐ ❝õ❛ ✭✷✳✽✮ ✈➔ sû ❞ö♥❣ ❣✐↔ t❤✐➳t✳
P❤➛♥ ❝❤ù♥❣ ♠✐♥❤ ❜➜t ✤➥♥❣ t❤ù❝✱ t❛ →♣ ❞ö♥❣ ✣à♥❤ ❧þ ✷✳✼ ❝❤♦ ❤➔♠ f (x) ❧➔ ❤➔♠ f (x) ✈➔ ❤➔♠ g(x)
❧➔ ❤➔♠ xf (x).
❱➼ ❞ö ✷✳✶✷✳ ❚➻♠
1
(1 + x2 )f 2 (x)dx
min
f ∈A
0
tr♦♥❣ ✤â
1
A = {f ∈ C[0, 1] :
f (x)dx = 1}
0
✈➔ t➻♠ ❤➔♠ f s❛♦ ❝❤♦ t❛ ♥❤➟♥ ✤÷ñ❝ ❣✐→ trà ♥❤ä ♥❤➜t✳
❍÷î♥❣ ❞➝♥✿ ⑩♣ ❞ö♥❣ ✣à♥❤ ❧þ ✷✳✼ ✈î✐ ❤➔♠ f (x) ❝❤➼♥❤ ❧➔ ❤➔♠ √1 + x2f (x) ✈➔ ❤➔♠ g(x) ❝❤➼♥❤ ❧➔
1
❤➔♠ √1+x
.
2
❱➼ ❞ö ✷✳✶✸✳ ❈❤ù♥❣ ♠✐♥❤ r➡♥❣ ♥➳✉ f ❧➔ ❤➔♠ ❧✐➯♥ tö❝ tr➯♥ [0, 1], ❦❤↔ ✈✐ tr➯♥ (0, 1), f (0) = 0 ✈➔
0 < f (x) ≤ 1
tr➯♥ (0, 1) t❤➻
1
2
1
f 3 (x)dx.
f (x)dx ≥
0
0
❈❤ù♥❣ ♠✐♥❤ r➡♥❣ ✤➥♥❣ t❤ù❝ ①↔② r❛ ❦❤✐ ✈➔ ❝❤➾ ❦❤✐ f (x) = x.
❱➼ ❞ö ✷✳✶✹✳ ❚➻♠
1
f 2 (x)dx
A := min
f ∈A
0
✶✻
tr♦♥❣ ✤â
1
A = {f ∈ R[0, 1] :
1
f (x)dx = 3,
0
xf (x)dx = 2}
0
✈➔ t➻♠ ❤➔♠ f s❛♦ ❝❤♦ t❛ ♥❤➟♥ ✤÷ñ❝ ❣✐→ trà ♥❤ä ♥❤➜t✳
P❤➙♥ t➼❝❤✿ ❚r♦♥❣ tr÷í♥❣ ❤ñ♣ ♥➔②✱ ❞♦ ✈➲ ❝ì ❜↔♥ t❛ ❦❤æ♥❣ ❝â t❤æ♥❣ t✐♥ ❣➻ ✈➲ ❤➔♠ f ❧î♥ ❤ì♥ ❤❛② ❜➨
❤ì♥ ❤➔♠ ❤♦➦❝ ❤➡♥❣ sè ♥➔♦ ♥➯♥ ✤➸ →♣ ❞ö♥❣ ✣à♥❤ ❧þ ✷✳✻ ♥â✐ ❝❤✉♥❣ s➩ r➜t ❦❤â✳ ❚r÷í♥❣ ❤ñ♣ ♥➔② t❛ t❤û
→♣ ❞ö♥❣ ✣à♥❤ ❧þ ✷✳✼ ✤➸ ❧➔♠✳ ❚❤æ♥❣ t❤÷í♥❣ ❝â t❤➸ ❝â ♠ët sè ❜↕♥ s✐♥❤ ✈✐➯♥ s➩ ❧➔♠ ♥❤÷ s❛✉✳ ❚❛ ❝â
2
1
9=
f (x)dx =
0
2
1
f (x) . . . 1dx
0
1
1
2
≤
12 dx
f (x)dx
0
0
1
f 2 (x)dx.
=
0
❉♦ ✤â A = 9. ❚✉② ♥❤✐➯♥ ❝❤ó þ r➡♥❣ ❝→❝❤ ❧➔♠ ♥➔② s➩ ❦❤æ♥❣ ✤ó♥❣✳ ▲þ ❞♦ ♥❤÷ s❛✉✿ ❚❛ ❦❤æ♥❣ t❤➸ t➻♠
✤÷ñ❝ ❤➔♠ f ♥➔♦ t❤ä❛ ♠➣♥ ✤✐➲✉ ❦✐➺♥ ✤➛✉ ❜➔✐ ✤➸ ❝❤♦ A = 9. ❱➻ ♥➳✉ ❦❤æ♥❣ t❤➻ ❦❤✐ ✤â t❛ ♣❤↔✐ ❝â
f (x) = α,
1
f (x)dx = 3,
0
1
xf (x)dx = 2,
0
✤✐➲✉ ♥➔② ❧➔ ✈æ ❧þ✳
✣è✐ ✈î✐ ❜➔✐ t♦→♥ t➻♠ ❣✐→ trà ❧î♥ ♥❤➜t ❤❛② ♥❤ä ♥❤➜t✱ ❝❤ó♥❣ t❛ ❝➛♥ ♣❤↔✐ t➻♠ ✤÷ñ❝ ❤➔♠ s❛♦ ❝❤♦ t❛
t❤➟t sü ♥❤➟♥ ✤÷ñ❝ ❣✐→ trà ♥❤ä ♥❤➜t ❤♦➦❝ ❧î♥ ♥❤➜t✳
✣è✐ ✈î✐ ❜➔✐ t♦→♥ tr➯♥✱ t❛ ❧➔♠ ♥❤÷ s❛✉✳
❈❤ù♥❣ ♠✐♥❤✳ ⑩♣ ❞ö♥❣ ✣à♥❤ ❧þ ✷✳✼✱ t❛ ❝â ✈î✐ ♠å✐ b ∈ R t❤➻
2
1
2
0
1
f 2 (x)dx ≥
1
2
(x + b)f (x)dx ≤
(2 + 3b) ≤
❉♦ ✤â
1
0
3(2 + 3b)2
,
3b2 + 3b + 1
0
∀b ∈ R.
0
❱➻ ✈➟②
1
f 2 (x)dx ≥ max
b∈R
0
f 2 (x)dx.
(x + b) dx
3(2 + 3b)2
= 12.
3b2 + 3b + 1
✶✼
✣➥♥❣ t❤ù❝ ①↔② r❛ ❦❤✐ ✈➔ ❝❤➾ ❦❤✐
3(2+3b)2
max 3b
2 +3b+1 = 12,
b∈R
f (x) = α(x + b),
1
f (x)dx = 3,
0
1
xf (x)dx = 2,
0
●✐↔✐ ❤➺ tr➯♥ t❛ t➻♠ ✤÷ñ❝ f (x) = 6x.
❱➼ ❞ö ✷✳✶✺✳ ❚➻♠
1
(f (x))2 dx
min
f ∈A
0
tr♦♥❣ ✤â
A = {f ∈ C 2 [0, 1] : f (0) = f (1) = 0, f (0) = a}
✈➔ t➻♠ ❤➔♠ f s❛♦ ❝❤♦ t❛ ♥❤➟♥ ✤÷ñ❝ ❣✐→ trà ♥❤ä ♥❤➜t✳
❍÷î♥❣ ❞➝♥✿ ⑩♣ ❞ö♥❣ ✣à♥❤ ❧þ ✷✳✼ ✈î✐ f (x) = 1 − x ❝á♥ g(x) = f
✷✳✸ ✣à♥❤ ❧þ ❣✐→ trà tr✉♥❣ ❜➻♥❤
✣è✐ ✈î✐ ❞↕♥❣ ❜➔✐ t➟♣ ♥➔②✱ ❝❤ó♥❣ t❛ ❝❤ó þ tî✐ ❝→❝ ✤à♥❤ ❧þ s❛✉✳
✣à♥❤ ❧þ ✷✳✶✻ ✭✣à♥❤ ❧þ ✮✳ ●✐↔ sû r➡♥❣✿
✭✐✮ ❤➔♠ f (x) ❧✐➯♥ tö❝ tr♦♥❣ [a, b],
✭✐✐✮
f (a)f (b) < 0.
❑❤✐ ✤â tç♥ t↕✐ c ∈ (a, b) s❛♦ ❝❤♦ f (c) = 0.
✣à♥❤ ❧þ ✷✳✶✼ ✭✣à♥❤ ❧þ ❘♦❧❧❡✮✳ ●✐↔ sû r➡♥❣
✭✐✮ ❤➔♠ f (x) ❧✐➯♥ tö❝ tr♦♥❣ [a, b],
✭✐✐✮ ❤➔♠ f (x) ❦❤↔ ✈✐ tr♦♥❣ (a, b).
✭✐✐✐✮
f (a) = f (b).
❑❤✐ ✤â tç♥ t↕✐ c ∈ (a, b) s❛♦ ❝❤♦ f (c) = 0.
✣à♥❤ ❧þ ✷✳✶✽ ✭✣à♥❤ ❧þ ▲❛❣r❛♥❣❡✮✳ ●✐↔ sû r➡♥❣
(x).
f (x) tử tr [a, b],
f (x) tr (a, b).
õ tỗ t c (a, b) s f (b) f (a) = f (c)(b a).
ỵ ỵ số f, g : [a, b] R. sỷ r
f (x), g(x) tử tr [a, b].
f (x), g(x) tr (a, b).
g (x) = 0
x (a, b).
õ tỗ t c (a, b) s
f (b)f (a)
g(b)g(a)
=
f (c)
g (c) .
t f số tử tr [a, b]. õ số F (x) =
x
số
tr [a, b]. r trữớ ủ f t ởt số ỳ t F (x)
tử tr [a, b].
f (t)dt
a
ử ự r f : [a, b] R số t õ tỗ t [a, b] s
b
f (t)dt.
f (t)dt =
a
P t ổ tữớ ố ợ t ú t sỷ ử ỵ
r ú t tỷ ử ỵ t ử ỵ
t t ỹ F ởt tr số t r tứ f
x
t õ t tợ t F (x) = f (t)dt, t tr trữớ ủ f t
a
F tử õ ử ỵ trỹ t F ổ t
t tử t t õ t ỹ õ t tứ F t ợ ởt
số s số ứ t t t õ t õ tr
t ởt ữ tỷ t s tỷ sỷ ử ỵ ờ
b
b
f (t)dt
f (t)dt =
a
ứ tt t s r
f (t)dt.
a
b
f (t)dt = 2
a
f (t)dt.
a
õ ự tr t ỗ t (a, b) s
b
f (t)dt = 2
a
f (t)dt.
a
✶✾
❚❤❛② θ ❜ð✐ x, ✈➔ t❛ ①➨t ❤➔♠
b
h(x) = 2F (x) −
f (t)dt,
a
tr♦♥❣ ✤â
x
F (x) =
✭✷✳✾✮
f (t)dt.
a
❚❛ ❝❤ó þ r➡♥❣
b
h(a)h(b) = 2F (a) −
f (t)dt 2F (b) −
a
= 0 −
b
a
a
f (t)dt
a
2
b
=−
b
f (t)dt −
f (t)dt 2
f (t)dt
a
b
b
f (t)dt ≤ 0.
a
◆❤÷ ✈➟②✱ ✤✐➲✉ ❦✐➺♥ ❝õ❛ ✣à♥❤ ❧þ ✷✳✶✻ ❝â t❤➸ →♣ ❞ö♥❣ ✤÷ñ❝✳ ❚ø ✤â✱ t❛ ❝â ❝→❝❤ ❣✐↔✐ ♥❤÷ s❛✉✳
❈❤ù♥❣ ♠✐♥❤✳ ✣➦t
b
h(x) = 2F (x) −
f (t)dt
a
tr♦♥❣ ✤â
x
F (x) =
x ∈ [a, b].
f (t)dt,
a
❑✐➸♠ tr❛ ✤÷ñ❝ h ❧➔ ❤➔♠ sè ❧✐➯♥ tö❝ tr➯♥ [a, b] ✈➔ t❤ä❛ ♠➣♥ ✤✐➲✉ ❦✐➺♥
b
−h(a) = h(b) =
f (t)dt.
a
❉♦ ✤â✱
2
b
h(a)h(b) = −
f (t)dt ≤ 0.
a
⑩♣ ❞ö♥❣ ✣à♥❤ ❧þ ✷✳✶✻✱ tç♥ t↕✐ θ ∈ (a, b) s❛♦ ❝❤♦ h(θ) = 0, tù❝ ❧➔
θ
b
f (t)dt =
a
f (t)dt.
θ
ử f : [a, b] R số tử sỷ r
tỗ t (a, b) s
b
f (t)dt = 0.
a
ự r
f (t)dt = f ().
a
P t ữỡ tỹ tr t tỷ ử ỵ r ự ụ
ợ F ữ tr t t õ F (x) = f (x) F (a) = F (b) õ ừ
ỵ ữủ tọ ử trỹ t ỵ t t ữủ tỗ
t (a, b) s F () = 0, tr t tỗ t (a, b) s F () = F ().
r trữớ ủ t t r ởt F (x) tt õ t ỹ tr
F (x). õ t ử ữủ ỵ t tỷ F (x) F (x) ợ ởt h(x) ữỡ
s tỗ t G(x) s G (x) = (F (x) F (x)) h(x). r trữớ ủ t õ t t
ữủ h(x) = ex , x [a, b]. õ ữ s
ự t G(x) = F (x)ex , tr õ F (x) ữủ ữ tr õ tứ tt
t õ
G(x)
tử tr [a, b],
G(x)
tr (a, b).
G(a) = G(b) = 0.
ử ỵ tỗ t (a, b) s G () = 0. t
G (x) = (F (x) F (x)) ex .
õ F () F ()
f (t)dt = f ().
a
ử f : [a, b] R số tử a > 0 sỷ r
r tỗ t (a, b) s
f (t)dt = f ().
a
ự ồ F (x) = x1
x
f (t)dt.
a
b
f (t)dt = 0.
a
ự
✷✶
❱➼ ❞ö ✷✳✷✹✳ ❈❤♦ f, g : [a, b] → R ❧➔ ❤❛✐ ❤➔♠ sè ❧✐➯♥ tö❝✳❈❤ù♥❣ ♠✐♥❤ r➡♥❣✱ tç♥ t↕✐ θ ∈ (a, b) s❛♦ ❝❤♦
b
b
a
a
❈❤ù♥❣ ♠✐♥❤✳ ❈❤å♥ ❤➔♠ F (x) =
g(t)dt.
f (t)dt = f (θ)
g(θ)
x
f (t)dt
a
✈➔ G(x) =
x
g(t)dt.
a
⑩♣ ❞ö♥❣ ✣à♥❤ ❧þ ✷✳✶✾✳
❱➼ ❞ö ✷✳✷✺✳ ❈❤♦ f, g : [a, b] → R ❧➔ ❤❛✐ ❤➔♠ sè ❧✐➯♥ tö❝✳❈❤ù♥❣ ♠✐♥❤ r➡♥❣✱ tç♥ t↕✐ θ ∈ (a, b) s❛♦ ❝❤♦
b
θ
f (t)dt = f (θ)
g(θ)
a
❈❤ù♥❣ ♠✐♥❤✳ ❈❤å♥ ❤➔♠ F (x) =
θ
b
x
g(t)dt.
f (t)dt
x
a
g(t)dt.
⑩♣ ❞ö♥❣ ✣à♥❤ ❧þ ✷✳✶✼✳
❱➼ ❞ö ✷✳✷✻✳ ❈❤♦ f, g : [a, b] → R ❧➔ ❤❛✐ ❤➔♠ sè ❞÷ì♥❣✱ ❧✐➯♥ tö❝✳❈❤ù♥❣ ♠✐♥❤ r➡♥❣✱ tç♥ t↕✐ θ ∈ (a, b)
s❛♦ ❝❤♦
f (θ)
−
θ
g(θ)
g(t)dt
f (t)dt
a
❈❤ù♥❣ ♠✐♥❤✳ ❈❤å♥ ❤➔♠ F (x) = e−x
= 1.
b
θ
x
b
f (t)dt g(t)dt.
a
x
⑩♣ ❞ö♥❣ ✣à♥❤ ❧þ ✷✳✶✼✳
▼ët sè ❜➔✐ t➟♣ →♣ ❞ö♥❣✳
✶✳ ❈❤♦ f : [0, 1] → [−1, 1] ❦❤↔ ✈✐ ❧✐➯♥ tö❝ tr➯♥ [0, 1] ✈➔ f (0) = f (1) = 1. ❈❤ù♥❣ ♠✐♥❤ r➡♥❣ tç♥ t↕✐
c ∈ (0, 1) s❛♦ ❝❤♦ f (x) = 2c tan f (c).
✷✳ ❈❤♦ ❤➔♠ sè
❧✐➯♥ tö❝ tr➯♥
(2013, 2015) s❛♦ ❝❤♦
f
[2013, 2015]
✈➔
2015
f (t)dt = 0.
2013
❈❤ù♥❣ ♠✐♥❤ r➡♥❣ tç♥ t↕✐
c ∈
c
2014
f (t)dt = cf (c).
2013
1
1
✸✳ ❈❤♦ f : [0, 1] → R ❧✐➯♥ tö❝ s❛♦ ❝❤♦ f (t)dt = tf (t)dt. ❈❤ù♥❣ ♠✐♥❤ r➡♥❣ tç♥ t↕✐ c ∈ (0, 1) s❛♦
0
0
❝❤♦
c
f (c) = 2014
f (t)dt.
0
b
✹✳ ❈❤♦ ❤➔♠ f ❧✐➯♥ tö❝ tr➯♥ [a, b] ✈➔ ❦❤↔ ✈✐ tr➯♥ (a, b) ✈î✐ a > 0 ✈➔ f (t)dt = 0.❈❤ù♥❣ ♠✐♥❤ r➡♥❣
a
tç♥ t↕✐ c ∈ (a, b) s❛♦ ❝❤♦
c
c
f (t)dt − 2013cf (c) + 2012
2014c
a
f (t)dt = 0.
a
✷✷
✺✳ ❈❤♦ ❤➔♠ sè f : [−1, 1] → R ❧✐➯♥ tö❝✳ ❈❤ù♥❣ ♠✐♥❤ r➡♥❣ ♣❤÷ì♥❣ tr➻♥❤
xf 2014 (x) − 2014f (x) = −2013x
❝â ♥❣❤✐➺♠ tr➯♥ ✤♦↕♥ [−1, 1].
✷✳✹ ◗✉② t➢❝ ▲✬❍♦s♣✐t❛❧
✣à♥❤ ❧þ ✷✳✷✼✳ ❈❤♦ I ❧➔ ❦❤♦↔♥❣ ♠ð ❦❤→❝ tr♦♥❣ R, ❣✐↔ sû x
✈➔ f, g : I → R ❧➔ ❤❛✐ ❤➔♠
∀x ∈ I. ●✐↔ sû r➡♥❣ ♠ët tr♦♥❣ ❤❛✐ ✤✐➲✉ ❦✐➺♥ s❛✉ ✤÷ñ❝ t❤ä❛
❦❤↔ ✈✐✱ ✈î✐ g ✤ì♥ ✤✐➺✉ t➠♥❣ ✈➔ g (x) =
♠➣♥
✶✳
f (x), g(x) → 0
✷✳
g(x) → ±∞
0
∈ R ∪ {±∞}
❦❤✐ x → x0 ,
❦❤✐ x → x0 . ❑❤✐ ✤â✱ ♥➳✉ ❣✐î✐ ❤↕♥
lim
x→x0
t❤➻ t❛ ❝â
f (x)
= l ∈ R ∪ {±∞}
g (x)
f (x)
= l.
x→x0 g(x)
lim
❱➼ ❞ö ✷✳✷✽✳ ❈❤♦ ❤➔♠ f ❧✐➯♥ tö❝ tr➯♥ (0, +∞) ✈➔
lim f (x) = 2016.
x→+∞
❚➼♥❤
x
1
lim
x→+∞ x
f (t)dt.
0
❈❤ù♥❣ ♠✐♥❤✳ ✣➸ →♣ ❞ö♥❣ q✉② t➢❝ ▲✬❍♦s♣✐t❛❧✱ t❛ ❝➛♥ ❝â ♣❤➨♣ ❝❤✐❛ ♠ët ❤➔♠ ❝❤♦ ♠ët ❤➔♠✳ ❚r♦♥❣
x
t❤÷í♥❣ ❤ñ♣ ♥➔②✱ t❛ ❝â t❤➸ t❤➜② ✤÷ñ❝ ♠ët ❤➔♠ ❧➔ f (t)dt ✈➔ ❤➔♠ ❝á♥ ❧↕✐ ❧➔ x. ⑩♣ ❞ö♥❣ ✣à♥❤ ❧þ ✷✳✷✼
❝❤♦ ❤➔♠ f (x) ð tr➯♥ ❝❤➼♥❤ ❧➔ ❤➔♠
0
x
f (t)dt,
0
❝á♥ ❤➔♠ g(x) ð ✣à♥❤ ❧þ tr➯♥ ❝❤➼♥❤ ❧➔ ❤➔♠ x. ❑❤✐ ✤â ❝→❝
✤✐➲✉ ❦✐➺♥ ❝õ❛ ✣à♥❤ ❧þ ✷✳✷✼ ✤➲✉ ✤÷ñ❝ t❤ä❛ ♠➣♥✱ ❤ì♥ ♥ú❛ ✈î✐ G(x) = x, F (x) =
F (x)
f (x)
=
= f (x).
G (x)
1
❉♦ ✤â✱ t❤❡♦ ❣✐↔ t❤✐➳t ✈➔ ✣à♥❤ ❧þ ✷✳✷✼ t❛ ❝â
x
1
lim
x→+∞ x
f (t)dt = lim f (x) = 2016.
x→+∞
0
❱➼ ❞ö ✷✳✷✾✳ ❈❤♦ f : (0, +∞) → R ❧➔ ❤➔♠ ❦❤↔ ✈✐ ❧✐➯♥ tö❝ ❝➜♣ ✷ s❛♦ ❝❤♦
|f (x) + 2xf (x) + (x2 + 1)f (x)| ≤ 1,
∀x ∈ R.
x
f (t)dt
0
t❤➻
✷✸
❈❤ù♥❣ ♠✐♥❤ r➡♥❣
lim f (x) = 0.
x→+∞
❱➼ ❞ö ✷✳✸✵✳
❱➼ ❞ö ✷✳✸✶✳