✣❸■ ❍➴❈ ❚❍⑩■ ◆●❯❨➊◆
❚❘×❮◆● ✣❸■ ❍➴❈ ❑❍❖❆ ❍➴❈
◆●❯❨➍◆ ◆●➴❈ ◗❯❨➌◆
✣➃◆● ❚❍Ù❈ ❱⑨ ❇❻❚ ✣➃◆● ❚❍Ù❈
❚❘❖◆● ▲❰P ❍⑨▼ ▲❖●❆❘■❚
▲❯❾◆ ❱❿◆ ❚❍❸❈ ❙➒ ❚❖⑩◆ ❍➴❈
❚❍⑩■ ◆●❯❨➊◆ ✲ ✷✵✷✵
✣❸■ ❍➴❈ ❚❍⑩■ ◆●❯❨➊◆
❚❘×❮◆● ✣❸■ ❍➴❈ ❑❍❖❆ ❍➴❈
◆●❯❨➍◆ ◆●➴❈ ◗❯❨➌◆
✣➃◆● ❚❍Ù❈ ❱⑨ ❇❻❚ ✣➃◆● ❚❍Ù❈
❚❘❖◆● ▲❰P ❍⑨▼ ▲❖●❆❘■❚
❈❤✉②➯♥ ♥❣➔♥❤✿ P❍×❒◆● P❍⑩P ❚❖⑩◆ ❙❒ ❈❻P
▼➣ sè✿ ✽ ✹✻ ✵✶ ✶✸
▲❯❾◆ ❱❿◆ ❚❍❸❈ ❙➒ ❚❖⑩◆ ❍➴❈
◆❣÷í✐ ❤÷î♥❣ ❞➝♥ ❦❤♦❛ ❤å❝✿
●❙✳❚❙❑❍✳ ◆❣✉②➵♥ ❱➠♥ ▼➟✉
❚❍⑩■ ◆●❯❨➊◆ ✲ ✷✵✷✵
✐
▼ö❝ ❧ö❝
▼Ð ✣❺❯
❈❤÷ì♥❣ ✶✳ ▼ët sè ❦✐➳♥ t❤ù❝ ❧✐➯♥ q✉❛♥ ✤➳♥ ❤➔♠ ❧♦❣❛r✐t
✶
✸
✶✳✶
▼ët sè t➼♥❤ ❝❤➜t ❝ì ❜↔♥ ❝õ❛ ❤➔♠ ❧♦❣❛r✐t ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳
✸
✶✳✷
✣➦❝ tr÷♥❣ ❝õ❛ ❤➔♠ t✉➛♥ ❤♦➔♥ ♥❤➙♥ t➼♥❤
✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳
✺
✶✳✷✳✶
❍➔♠ t✉➛♥ ❤♦➔♥ ♥❤➙♥ t➼♥❤ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳
✺
✶✳✷✳✷
❍➔♠ ♣❤↔♥ t✉➛♥ ❤♦➔♥ ♥❤➙♥ t➼♥❤
✻
✶✳✷✳✸
❈→❝ ❜➔✐ t♦→♥ ❧✐➯♥ q✉❛♥ ✤➳♥ ❤➔♠ t✉➛♥ ❤♦➔♥ ♥❤➙♥ t➼♥❤
✶✳✸
✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳
▼ët sè ✤à♥❤ ❧➼ ❧✐➯♥ q✉❛♥ ✤➳♥ ❧î♣ ❤➔♠ ❧ç✐ ✈➔ ❤➔♠ ❧ç✐ ❧♦❣❛r✐t ✳
✽
✾
❈❤÷ì♥❣ ✷✳ ✣➥♥❣ t❤ù❝ ✈➔ ♣❤÷ì♥❣ tr➻♥❤ s✐➯✉ ✈✐➺t ❞↕♥❣ ❧♦❣❛r✐t ✶✹
✷✳✶
P❤÷ì♥❣ tr➻♥❤ ❤➔♠ ❈❛✉❝❤② ❞↕♥❣ ❧♦❣❛r✐t
✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳
✶✹
✷✳✷
P❤÷ì♥❣ tr➻♥❤ s✐➯✉ ✈✐➺t ❞↕♥❣ ❧♦❣❛r✐t ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳
✷✷
✷✳✸
❍➺ ♣❤÷ì♥❣ tr➻♥❤ ❧♦❣❛r✐t ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳
✸✹
✷✳✸✳✶
P❤➨♣ ❝❤✉②➸♥ ✈➲ ❤➺ ✤↕✐ sè ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳
✸✹
✷✳✸✳✷
❙û ❞ö♥❣ t➼♥❤ ✤ì♥ ✤✐➺✉ ❝õ❛ ❤➔♠ sè ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳
✸✻
❈❤÷ì♥❣ ✸✳ ❇➜t ✤➥♥❣ t❤ù❝ tr♦♥❣ ❧î♣ ❤➔♠ ❧♦❣❛r✐t
✸✳✶
✸✳✷
✸✽
❈→❝ ❞↕♥❣ t♦→♥ ÷î❝ ❧÷ñ♥❣ ✈➔ ❜➜t ✤➥♥❣ t❤ù❝ ❧♦❣❛r✐t
✳ ✳ ✳ ✳ ✳
✸✽
✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳
✸✽
✸✳✶✳✶
❇➜t ✤➥♥❣ t❤ù❝ ❤➔♠ ❧♦❣❛r✐t
✸✳✶✳✷
P❤÷ì♥❣ ♣❤→♣ ❣✐↔✐ ❜➜t ✤➥♥❣ t❤ù❝ ❝❤ù❛ ❧♦❣❛r✐t
✳ ✳ ✳ ✳
✹✹
✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳
✺✶
✸✳✷✳✶
❇➔✐ t♦→♥ ❝ü❝ trà ❧✐➯♥ q✉❛♥ ✤➳♥ ❤➔♠ ❧♦❣❛r✐t ✳ ✳ ✳ ✳ ✳ ✳
✺✶
✸✳✷✳✷
❇➜t ✤➥♥❣ t❤ù❝ tr♦♥❣ ❞➣② sè ✈➔ ❣✐î✐ ❤↕♥
✺✻
✸✳✷✳✸
Ù♥❣ ❞ö♥❣ ❤➔♠ ❧ç✐✱ ❤➔♠ ❧♦❣❛r✐t tr♦♥❣ ❝❤ù♥❣ ♠✐♥❤
▼ët sè t➼♥❤ t♦→♥ ❦❤→❝ ❧✐➯♥ q✉❛♥
✳ ✳ ✳ ✳ ✳ ✳ ✳
❝→❝ ❜➜t ✤➥♥❣ t❤ù❝ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳ ✳
❑➳t ❧✉➟♥
✻✵
✻✻
t tự õ tr t q trồ tr t ồ ởt ở
q trồ ừ t số tự t tự tr
ợ rt ởt tr ỳ ở ỡ q trồ ừ
ữỡ tr t tr ồ ờ tổ tr ữỡ
tr ỗ ữù ợ P ử ử ý t qố
ỹ
t tr t ồ s ọ t t
q tợ t t ừ rt tữớ ữủ ỳ
t tữớ ữủ tở õ ỏ ọ tữ
s õ ổ õ sự t út sỹ t tỏ
õ s t ừ ồ s
ự ỗ ữù ỗ ữù ồ s ọ
rt tổ ồ t tự t
tự tr ợ rt
t st ởt số ợ t tứ t ố
t t tr ữợ ỳ
trú ỗ ữỡ t
ữỡ ởt số tự q rt r ữỡ
t tr ởt số t t ỡ ừ rt trữ
ừ t t ởt số q ợ ỗ
ỗ rt
ữỡ r tự rt tr ợ số ờ
ữủ tr tổ q ởt số t sỷ ử ữỡ tr
ữỡ tr rt ố ữỡ
tr ữỡ ữỡ tr s t rt
ũ ợ ử tữỡ ự
ữỡ t tự tr ợ rt ữỡ tr
t tự rt ữỡ t tự ự
rt tổ q ử ử t r ỏ tr ự ử
ừ t ỹ tr rt ụ ữ
t t ợ ự ử ỗ rt tr ự ởt
ợ t tự
ữủ t t rữớ ồ ồ ồ
ữợ sỹ ữợ ừ sữ s ồ
tọ ỏ t ỡ s s ố ợ ữớ
t t ữợ tr t tự ự
t tr sốt q tr ồ t t ụ
tọ ỏ t ỡ t tợ ổ tr
trữớ ồ ồ ồ ú ù
t t tr sốt tớ ồ t t rữớ
ỗ tớ tổ ụ ỷ ớ ỡ tợ ỗ
ổ ú ù ở tổ tr q tr t
t
ồ
✸
❈❤÷ì♥❣ ✶✳ ▼ët sè ❦✐➳♥ t❤ù❝ ❧✐➯♥
q✉❛♥ ✤➳♥ ❤➔♠ ❧♦❣❛r✐t
▼ö❝ ✤➼❝❤ ❝õ❛ ❝❤÷ì♥❣ ♥➔② ❧➔ tr➻♥❤ ❜➔② ♠ët sè t➼♥❤ ❝❤➜t ❝ì ❜↔♥ ❝õ❛ ❤➔♠
❧♦❣❛r✐t❀ ✤➦❝ tr÷♥❣ ❝õ❛ ❤➔♠ t✉➛♥ ❤♦➔♥ ♥❤➙♥ t➼♥❤ ✈➔ ♠ët sè ✤à♥❤ ❧➼ ❧✐➯♥
q✉❛♥ ✤➳♥ ❧î♣ ❤➔♠ ❧ç✐ ✈➔ ❤➔♠ ❧ç✐ ❧♦❣❛r✐t✳ ❈→❝ ❦➳t q✉↔ ❝❤➼♥❤ ❝õ❛ ❝❤÷ì♥❣
✤÷ñ❝ t❤❛♠ ❦❤↔♦ tø ❝→❝ t➔✐ ❧✐➺✉ ❬✶❪✱ ❬✷❪✳
✶✳✶ ▼ët sè t➼♥❤ ❝❤➜t ❝ì ❜↔♥ ❝õ❛ ❤➔♠ ❧♦❣❛r✐t
✣à♥❤ ♥❣❤➽❛ ✶✳✶✳ a > 0, a = 1
f (x) = loga x
❈❤♦
❤➔♠ sè ❧♦❣❛r✐t
✳ ❑❤✐ ✤â ❤➔♠ sè
✤÷ñ❝
a✳
log x
x
❚ø ✤à♥❤ ♥❣❤➽❛ ♥➔② t❛ s✉② r❛✿ loga a = 1✱ loga 1 = 0✱ x = a a ✱ x = loga a ✳
❣å✐ ❧➔
❝ì sè
❚r♦♥❣ ❝→❝ ♣❤➛♥ t✐➳♣ t❤❡♦✱ t❛ ❣✐↔ sû
◆❤➟♥ ①➨t ✶✳✶✳
D = (0; +∞)
✐✮ ❍➔♠ sè ❧♦❣❛r✐t ❝â t➟♣ ①→❝ ✤à♥❤
✐✐✮ ❍➔♠ sè
f (x) = loga x
f (x) = loga x
✳
✭❚➼♥❤ ✤ì♥ ✤✐➺✉✮
ln a > 0
a>1
1
.
x ln a
a > 1✳
♥➯♥ s✉② r❛
f (x) = loga x
0 < a < 1✳
t❤➻
✲ ❚r÷í♥❣ ❤ñ♣ ✷✿
❤ì♥ ♥ú❛
❚❛ ❦❤↔♦ s→t t➼♥❤ ✤ì♥ ✤✐➺✉ ❝õ❛ ❤➔♠ sè
f (x) = (loga x) =
❱➟②✱ ❦❤✐
I = R✳
x > 0✱
tr♦♥❣ ✷ tr÷í♥❣ ❤ñ♣✳
✲ ❚r÷í♥❣ ❤ñ♣ ✶✿
❑❤✐ ✤â✱
✈➔ t➟♣ ❣✐→ trà
❧✐➯♥ tö❝ ✈➔ ❝â ✤↕♦ ❤➔♠ ✈î✐ ♠å✐
f (x) =
❚➼♥❤ ❝❤➜t ✶✳✶
0 < a = 1✳
1
> 0, ∀x > 0.
x ln a
❧➔ ❤➔♠ ✤ç♥❣ ❜✐➳♥ tr➯♥ ❉✳
✹
❚r♦♥❣ tr÷í♥❣ ❤ñ♣ ♥➔②
loga x
f (x) < 0, ∀x ∈ D✳
❱➟②✱ ❦❤✐
0
t❤➻
f (x) =
❧➔ ❤➔♠ sè ♥❣❤à❝❤ ❜✐➳♥ tr➯♥ ❉✳
❚➼♥❤ ❝❤➜t ✶✳✷
✳
y = loga x, a > 0, a = 1, x > 0✱
✭❚➼♥❤ ❧ç✐✱ ❧ã♠✮ ❳➨t ❤➔♠ sè
t❛ ❝â
f (x) = (loga x) =
f (x) =
✲ ◆➳✉
✲ ◆➳✉
−1
.
x2 ln a
1
,
x ln a
a > 1 tù❝ ln a > 0 t❤➻ y < 0 s✉② r❛ ❤➔♠ sè ❧ã♠ tr➯♥ (0; +∞)✳
0 < a < 1 tù❝ ln a < 0 t❤➻ y > 0 s✉② r❛ ❤➔♠ sè ❧ç✐ tr➯♥ (0; +∞)✳
❚➼♥❤ ❝❤➜t ✶✳✸✳
❱î✐ ♠å✐
a > 0, a = 1
✈➔
❚➼♥❤ ❝❤➜t ✶✳✹✳
❱î✐ ♠å✐
a > 0✱ a = 1
✈➔
x1 , x2 ∈ (0; +∞)✱ t❛ ❝â
x1
loga (x1 x2 ) = loga x1 + loga x2 , loga
= loga x1 − loga x2 .
x2
loga xα = αloga x, loga x =
❚➼♥❤ ❝❤➜t ✶✳✺✳
❱î✐ ♠å✐
x > 0✳
❱î✐ ♠å✐
0 < a = 1, b = 1
✈➔
x > 0✱
0 < a = 1, 0 < c = 1
loga x =
❚➼♥❤ ❝❤➜t ✶✳✼✳
❍➔♠ sè
❚➼♥❤ ❝❤➜t ✶✳✽✳
❱î✐ ♠å✐
α
❜➜t ❦ý✱ t❛ ❝â
1
loga xα = α logaα x = logaα xα .
α
loga b. logb c = loga c, loga b =
❚➼♥❤ ❝❤➜t ✶✳✻✳
❱î✐
t❛ ❝â
1
.
logb a
✈➔
x > 0✱
t❛ ❝â
logc x
.
logc a
f (x) = loga x (0 < a = 1) ❝â ✤↕♦ ❤➔♠ t↕✐ ♠å✐
1
. ◆➳✉ ❤➔♠ sè u = u(x) ❝â ✤↕♦ ❤➔♠
✤✐➸♠ x ∈ (0; +∞) ✈➔ (loga x) =
x ln a
tr➯♥ ❦❤♦↔♥❣ J ∈ R t❤➻ ❤➔♠ sè y = loga u(x)✱ (0 < a = 1) ❝â ✤↕♦ ❤➔♠ tr➯♥
u (x)
J ✈➔ (loga u(x)) =
.
u(x) ln a
✐✮ ❑❤✐
✐✐✮ ❑❤✐
a>1
t❤➻
a > 0✱ a = 1
✈➔
x1 , x2 ∈ (0; +∞)✱
loga x1 < loga x2 ⇔ x1 < x2 .
0
t❤➻
loga x1 < loga x2 ⇔ x1 > x2 .
t❛ ❝â
✺
✶✳✷ ✣➦❝ tr÷♥❣ ❝õ❛ ❤➔♠ t✉➛♥ ❤♦➔♥ ♥❤➙♥ t➼♥❤
❚r♦♥❣ ❝❤÷ì♥❣ tr➻♥❤ ❣✐↔✐ t➼❝❤ t❛ t❤÷í♥❣ ❧➔♠ q✉❡♥ ✈î✐ ❧î♣ ❤➔♠ ❧÷ñ♥❣ ❣✐→❝
❧➔ ♥❤ú♥❣ ❤➔♠ t✉➛♥ ❤♦➔♥ ✭❝ë♥❣ t➼♥❤✮ q✉❡♥ t❤✉ë❝✳ ❘➜t ♥❤✐➲✉ ♣❤÷ì♥❣ tr➻♥❤
❤➔♠ ✈➔ ❝→❝ ❞↕♥❣ t♦→♥ ❧✐➯♥ q✉❛♥ ✤á✐ ❤ä✐ ❝➛♥ t➻♠ ❤✐➸✉ t❤➯♠ ❝→❝ t➼♥❤ ❝❤➜t
✈➔ ✤➦❝ tr÷♥❣ ❝õ❛ ❧î♣ ❤➔♠ t✉➛♥ ❤♦➔♥ ✈➔ ♣❤↔♥ t✉➛♥ ❤♦➔♥ ♥❤➙♥ t➼♥❤ ❣➢♥ ✈î✐
❤➔♠ ❧♦❣❛r✐t✳
✶✳✷✳✶ ❍➔♠ t✉➛♥ ❤♦➔♥ ♥❤➙♥ t➼♥❤
✣à♥❤ ♥❣❤➽❛ ✶✳✷✳
❦ý
a; (a > 1)
❍➔♠ sè
M
tr➯♥
♥➳✉
f (x) ✤÷ñ❝ ❣å✐
M ⊂ D(f ) ✈➔
❧➔
❤➔♠ t✉➛♥ ❤♦➔♥ ♥❤➙♥ t➼♥❤
❝❤✉
∀x ∈ M s✉② r❛ a±1 x ∈ M
f (ax) = f (x), ∀x ∈ M.
❱➼ ❞ö ✶✳✶✳
f (x) = sin(2π log2 x)✳ ❑❤✐ ✤â f (x) ❧➔ ❤➔♠ t✉➛♥ ❤♦➔♥
+
+
±1
+
❦ý ✷ tr➯♥ R ✳ ❚❤➟t ✈➟②✱ t❛ ❝â ∀x ∈ R t❤➻ 2 x ∈ R ✈➔
❳➨t
♥❤➙♥ t➼♥❤ ❝❤✉
f (2x) = sin(2π log2 (2x))
= sin(2π(1 + log2 x))
= sin(2π log2 x) = f (x).
❚➼♥❤ ❝❤➜t ✶✳✾✳
◆➳✉
❦ý t÷ì♥❣ ù♥❣ ❧➔
a
f (x)
✈➔
b
✈➔
tr➯♥
g(x)
M
✈➔
❧➔ ❤❛✐ ❤➔♠ t✉➛♥ ❤♦➔♥ ♥❤➙♥ t➼♥❤ ❝❤✉
ln |a|
m
= , m, n ∈ N∗
ln |b|
n
t❤➻
F (x) =
f (x) + g(x) ✈➔ G(x) = f (x).g(x) ❧➔ ❝→❝ ❤➔♠ t✉➛♥ ❤♦➔♥ ♥❤➙♥ t➼♥❤ tr➯♥ M ✳
❈❤ù♥❣ ♠✐♥❤✳
ln |a|
m
n
m
=
s✉② r❛ |a| = |b| ✳
ln |b|
n
❝õ❛ F (x) ✈➔ G(x)✳ ❚❤➟t ✈➟②✱ t❛
❚ø ❣✐↔ t❤✐➳t
T := a2n = b2m
❧➔ ❝❤✉ ❦ý
❚❛ ❝❤ù♥❣ ♠✐♥❤
❝â
F (T x) = f (a2n x) + g(b2m x) = f (x) + g(x) = F (x), ∀x ∈ M ;
G(T x) = f (a2n x)g(b2m x) = f (x)g(x) = G(x), ∀x ∈ M.
∀x ∈ M, T ±1 x ∈ M ✳
t➼♥❤ tr➯♥ M ✳
❍ì♥ ♥ú❛✱
♥❤➙♥
❚➼♥❤ ❝❤➜t ✶✳✶✵✳
tr➯♥
tr➯♥
R t❤➻
R+ ✳
❉♦ ✤â✱
F (x), G(x)
❧➔ ❝→❝ ❤➔♠ t✉➛♥ ❤♦➔♥
f (x) ❧➔ ❤➔♠ t✉➛♥ ❤♦➔♥ ❝ë♥❣ t➼♥❤ ❝❤✉ ❦ý a✱ a > 0
g(t) = f (ln t)✱ ✭t > 0✮ ❧➔ ❤➔♠ t✉➛♥ ❤♦➔♥ ♥❤➙♥ t➼♥❤ ❝❤✉ ❦ý ea
◆➳✉
✻
f (x) ❧➔ ❤➔♠ t✉➛♥ ❤♦➔♥ ♥❤➙♥ t➼♥❤ ❝❤✉ ❦ý a ✭a > 1✮
g(t) = f (et ) ❧➔ ❤➔♠ t✉➛♥ ❤♦➔♥ ❝ë♥❣ t➼♥❤ ❝❤✉ ❦ý ln a tr➯♥ R✳
◆❣÷ñ❝ ❧↕✐✱ ♥➳✉
R+
t❤➻
❈❤ù♥❣ ♠✐♥❤✳ ●✐↔ sû f (x) ❧➔ ❤➔♠ t✉➛♥
tr➯♥ R✳ ❳➨t g(t) = f (ln t)✱ ✭t > 0✮✳
❤♦➔♥ ❝ë♥❣ t➼♥❤ ❝❤✉ ❦ý
tr➯♥
a✱ a > 0
❚❛ ❝â
g(ea t) = f (ln(ea t)) = f (ln ea + ln t)
= f (a + ln t) = f (ln t) = g(t), ∀t ∈ R+ .
❱➟②
g(t)
◆❣÷ñ❝
✭0
❧➔ ❤➔♠ t✉➛♥ ❤♦➔♥ ♥❤➙♥ t➼♥❤ ❝❤✉ ❦ý
❧↕✐✱
❣✐↔
sû
f (x)
❧➔
< a = 1✮ tr➯♥ R+ ✳
t
❳➨t g(t) = f (e ), ∀t ∈ R✳
❤➔♠
t✉➛♥
ea
tr➯♥
❤♦➔♥
R+ ✳
♥❤➙♥
t➼♥❤
❝❤✉
❦ý
a
❚❛ ❝â
g(t + ln a) = f (et+ln a ) = f (et .eln a )
= f (aet ) = f (et ) = g(t), ∀t ∈ R.
❱➟②
g(t)
❧➔ ❤➔♠ t✉➛♥ ❤♦➔♥ ❝ë♥❣ t➼♥❤ ❝❤✉ ❦ý
ln a
tr➯♥
R✳
✶✳✷✳✷ ❍➔♠ ♣❤↔♥ t✉➛♥ ❤♦➔♥ ♥❤➙♥ t➼♥❤
✣à♥❤ ♥❣❤➽❛ ✶✳✸✳
❝❤✉ ❦ý
f (x) ✤÷ñ❝ ❣å✐ ❧➔ ❤➔♠ ♣❤↔♥ t✉➛♥ ❤♦➔♥ ♥❤➙♥ t➼♥❤
a (a > 1) tr➯♥ M ♥➳✉ M ⊂ D(f ) ✈➔
∀x ∈ M s✉② r❛ a±1 x ∈ M
f (ax) = −f (x), ∀x ∈ M.
❱➼ ❞ö ✶✳✷✳
❍➔♠ sè
f (x) = cos(π log2 x)✳ ❑❤✐ ✤â f (x) ❧➔ ❤➔♠ ♣❤↔♥ t✉➛♥ ❤♦➔♥
+
❦ý 2 tr➯♥ R ✳
❳➨t
♥❤➙♥ t➼♥❤ ❝❤✉
❚❤➟t ✈➟②✱ t❛ ❝â
∀x ∈ R+
t❤➻
f (2x) = cos(π log2 (2x)) = cos(π+π log2 x) = − cos(π log2 x) = −f (x), ∀x ∈ R+ .
❱➼ ❞ö ✶✳✸✳
√
1
[sin(2π log2 ( 2x)) − sin(2π log2 x)]✳
2
√
f (x) ❧➔ ❤➔♠ ♣❤↔♥ t✉➛♥ ❤♦➔♥ ♥❤➙♥
t➼♥❤ ❝❤✉ ❦ý
2 tr➯♥ R+ ✳
√
+
±1
+
❚❤➟t ✈➟②✱ t❛ ❝â ∀x ∈ R t❤➻ ( 2) x ∈ R ✈➔
√
√
1
f ( 2x) = [sin(2π log2 (2x)) − sin(2π log2 ( 2x))]
2
❳➨t
f (x) =
❑❤✐ ✤â
✼
√
1
= [sin(2π(1 + log2 x)) − sin(2π log2 ( 2x))]
2
√
1
= [sin(2π log2 x) − sin(2π log2 ( 2x))] = −f (x).
2
❚➼♥❤ ❝❤➜t ✶✳✶✶✳
▼å✐ ❤➔♠ ♣❤↔♥ t✉➛♥ ❤♦➔♥ ♥❤➙♥ t➼♥❤ tr➯♥
t✉➛♥ ❤♦➔♥ ♥❤➙♥ t➼♥❤ tr➯♥
❈❤ù♥❣ ♠✐♥❤✳
M
✤➲✉ ❧➔ ❤➔♠
M✳
❚❤❡♦ ❣✐↔ t❤✐➳t tç♥ t↕✐
b > 1 s❛♦ ❝❤♦ ∀x ∈ M
t❤➻
b±1 ∈ M
✈➔
f (bx) = −f (x), ∀x ∈ M.
❙✉② r❛✱
∀x ∈ M
t❤➻
b±1 ∈ M
✈➔
f (b2 x) = f (b(bx)) = −f (bx) = −(−f (x)) = f (x), ∀x ∈ M.
◆❤÷ ✈➟②✱
f (x)
❧➔ ❤➔♠ t✉➛♥ ❤♦➔♥ ♥❤➙♥ t➼♥❤ ❝❤✉ ❦ý
❚➼♥❤ ❝❤➜t ✶✳✶✷✳ f (x)
tr➯♥
M
❦❤✐ ✈➔ ❝❤➾ ❦❤✐
b2
tr➯♥
M✳
❧➔ ❤➔♠ ♣❤↔♥ t✉➛♥ ❤♦➔♥ ♥❤➙♥ t➼♥❤ ❝❤✉ ❦ý
f (x)
b ✭b > 1✮
❝â ❞↕♥❣✿
1
f (x) = (g(bx) − g(x)),
2
tr♦♥❣ ✤â✱
g(x)
❧➔ ❤➔♠ t✉➛♥ ❤♦➔♥ ♥❤➙♥ t➼♥❤ ❝❤✉ ❦ý
b2
tr➯♥
M✳
❈❤ù♥❣ ♠✐♥❤✳ ✭✐✮ ●✐↔ sû f ❧➔ ❤➔♠ ♣❤↔♥ t✉➛♥ ❤♦➔♥ ♥❤➙♥ t➼♥❤ ❝❤✉ ❦ý b tr➯♥
M ✳ ❑❤✐ ✤â g(x) = −f (x) ❧➔ ❤➔♠ t✉➛♥ ❤♦➔♥ ♥❤➙♥ t➼♥❤ ❝❤✉ ❦ý b2 tr➯♥ M
✈➔
✭✐✐✮
1
1
(g(bx) − g(x)) = (−f (bx) − (−f (x)))
2
2
1
= (−(−f (x)) + f (x)) = f (x), ∀x ∈ M.
2
1
◆❣÷ñ❝ ❧↕✐✱ f (x) = (g(bx) − g(x)), t❤➻
2
1
1
f (bx) = (g(b2 x) − g(bx)) = (g(x) − g(bx))
2
2
1
= − (g(bx) − g(x)) = −f (x), ∀x ∈ M.
2
∀x ∈ M
tr➯♥ M ✳
❍ì♥ ♥ú❛✱
♥❤➙♥ t➼♥❤
t❤➻
b±1 x ∈ M ✳
❉♦ ✤â✱
f (x)
❧➔ ❤➔♠ ♣❤↔♥ t✉➛♥ ❤♦➔♥
✽
✶✳✷✳✸ ❈→❝ ❜➔✐ t♦→♥ ❧✐➯♥ q✉❛♥ ✤➳♥ ❤➔♠ t✉➛♥ ❤♦➔♥ ♥❤➙♥ t➼♥❤
❇➔✐ t♦→♥ ✶✳✶✳
❈❤♦
a > 1✳
❳→❝ ✤à♥❤ t➜t ❝↔ ❝→❝ ❤➔♠
f (x)
t❤ä❛ ♠➣♥ ✤✐➲✉
❦✐➺♥
f (ax) = f (x), ∀x ∈ R+ .
▲í✐ ❣✐↔✐
✳
✣➦t
x = at
✈➔
f (at ) = h1 (t)✳
❑❤✐ ✤â
t = loga x
✈➔
f (ax) = f (x) ⇔ h1 (t + 1) = h1 (t), ∀t ∈ R,
h(t) = f (at ).
x < 0✳ ✣➦t −x = at
tr♦♥❣ ✤â
❳➨t
✈➔
f (−at ) = h2 (t)✳
❑❤✐ ✤â
t = loga |x|
✈➔
f (ax) = f (x) ⇔ h2 (t + 1) = h2 (t), ∀t ∈ R.
f (x) = h(loga |x|)
❦ý ✶ tr➯♥ R✳
❑➳t ❧✉➟♥✿
tò② þ ❝❤✉
❇➔✐ t♦→♥ ✶✳✷✳
❈❤♦
tr♦♥❣ ✤â
a < 0, a = −1✳
h(t)
❧➔ ❤➔♠ t✉➛♥ ❤♦➔♥ ❝ë♥❣ t➼♥❤
❳→❝ ✤à♥❤ t➜t ❝↔ ❝→❝ ❤➔♠
f (x)
t❤ä❛
♠➣♥ ✤✐➲✉ ❦✐➺♥
f (ax) = −f (x), ∀x ∈ R.
▲í✐ ❣✐↔✐
✳ ❚ø ✤✐➲✉ ❦✐➺♥ ❝õ❛ ❜➔✐ t♦→♥ s✉② r❛
f (a2 x) = f (x), ∀x ∈ R.
❱➟②✱ ♠å✐ ♥❣❤✐➺♠ ❝õ❛ ❜➔✐ t♦→♥ ❝â ❞↕♥❣
1
f (x) = [g(x) − g(ax)],
2
tr♦♥❣ ✤â
g(a2 x) = g(x), ∀x ∈ R.
❚❤➟t ✈➟②✱ ♥➳✉
f (x)
❝â ❞↕♥❣ tr➯♥ t❤➻ t❛ ❝â
1
f (ax) = [g(ax) − g(a2 x)]
2
◆❣÷ñ❝ ❧↕✐✱ ✈î✐ ♠é✐
1
[g(ax) − g(x)] = −f (x), ∀x ∈ R.
2
f (x) t❤ä❛ ♠➣♥ ✤✐➲✉ ❦✐➺♥ ❜➔✐ t♦→♥✱
❑❤✐ ✤â
g(a2 x) = g(x), ∀x ∈ R.
❝❤å♥
g(x) = f (x)✳
1
1
[g(x) g(ax)] = [f (x) f (ax)]
2
2
1
= [f (x) + f (x)] = f (x), x R.
2
r t
1
f (x) = [g(x) g(ax)],
2
tr õ
ợ
1
h
log|a| x x > 0
1
2
g(x) = d tũ ỵ x = 0
1
h2 log|a| |x| x < 0
2
h1 (t) h2 (t)
t ở t tũ ỵ ý tr
R
ởt số q ợ ỗ ỗ rt
ỵ
số f : [a; b] R tọ tử tr
[a; b] õ tr (a; b) f (a) = f (b) t tỗ t c (a; b)
s f (c) = 0
ỵ
r
số f : [a; b] R tọ tử
tr [a; b] tr (a; b) õ tỗ t c (a; b) s
f (c) =
ỵ
f (b) f (a)
.
ba
sỷ x > 1 õ
t tự r
(1 + x) 1 + x 0 1
(1 + x) 1 + x 0 1.
[a, b]
ợ ồ
f : [a, b] R ồ ỗ
x, y [a, b] ồ [0, 1] t õ
số tỹ
tr
f (x + (1 )y) f (x) + (1 )f (y).
tr t õ t tự t t t õ t
õ
ỗ
f
ỗ tỹ sỹ
f
t õ õ ó
f
ỵ
f
: (a, b) R ỗ
tr (a, b) n N 1 , 2 , . . . , n (0, 1) số tỹ tọ
1 + 2 + ã ã ã + n = 1. õ ợ ồ x1 , x2 , . . . , xn (a, b) t õ
t tự s
n
n
f
i xi
i f (xi ),
i=1
i=1
f (1 x1 + 2 x2 + ã ã ã + n xn ) 1 f (x1 ) + 2 f (x2 ) + ã ã ã + n f (xn ).
ỵ
t tự rt ố ợ rt
số {xk , yk I(a, b), k = 1, 2, . . . , n} ợ 0 < a < b tọ
x1 x2 ã ã ã xn , y1 y2 ã ã ã yn
x1 y1 ,
x1 + x2 y1 + y2 ,
......
x1 + x2 + ã ã ã + xn1 y1 + y2 + ã ã ã + yn1 ,
x + x + ããã + x = y + y + ããã + y .
1
2
n
1
2
n
õ ự ợ f (x) = logd x ợ d > 1 t õ
f (x1 ) + f (x2 ) + ã ã ã + f (xn ) f (y1 ) + f (y2 ) + ã ã ã + f (yn ).
ợ số ữỡ
r ở
a, b
r số ồ
A(a, b) =
r
a+b
.
2
r ồ
G(a, b) =
t
ab.
r ỏ
H(a, b) =
2ab
2
=
.
1 1
a+b
+
a b
rữớ ủ ỵ
ợ
n
a = {ak }nk=1
ừ
n
số ổ
số ữỡ ố t ỵ
1
A(a) =
n
n
n
n
1/n
ak , H(a) =
ak , G(a) =
n
k=1
k=1
k=1
.
a1
k
A(a), G(a), H(a) tữỡ ự ữủ ồ tr ở
tr tr ỏ ừ số a1 , a2 , . . . , an .
ữủ
ợ số ổ
a, b
ar + b r
Mr (a, b) =
2
ữủ
Mr (a, b)
ữủ ồ
r=0
1
r
t ỵ
.
tr ụ tứ
ừ số
a
b.
ố
ợ trữớ ủ ú t ỵ
a=
ữủ
{ak }nk=1 (ak
Mr (a)
1
0), Mr (a) =
n
n
ark
1
r
, r = 0.
k=1
ữủ ồ tr ụ tứ ừ số
ỵ ợ số ữỡ a
a1 , a2 , ..., an .
= {ak }nk=1 , r1 < r2 t Mr1 (a) <
Mr2 (a). tự r a1 = a2 = ... = an .
ừ số
a, b
ợ số ữỡ
a, b
t
tr rt
tự
L(a, b) =
ba
, a = b,
ln b ln a
L(a, a) = a.
t r
L(a, b) =
1
1
ba
b
a
dx
x
1
=
M1
1
, (a, b)
x
.
ỵ ợ số ữỡ a < b õ t tự
H(a, b) < G(a, b) < L(a, b) < A(a, b).
ự
0 < a < b f (x) = ex
[ln a, ln b]. õ t tự
sỷ
ỗ tr
ln a + ln b
2
e
(ln b ln a) <
ln b
ex dx <
ln a
ỗ tr
R,
ln a + ln b
(ln b ln a).
2
õ
✶✷
❚ø ✤➙② s✉② r❛
√
ab <
b−a
a+b
<
⇔ G(a, b) < L(a, b) < A(a, b).
ln b − ln a
2
❚❛ ❝â
√
2ab
< ab ⇔ H(a, b) < G(a, b).
a+b
❱➟②
H(a, b) < G(a, b) < L(a, b) < A(a, b), a, b > 0, a = b.
✣à♥❤ ❧þ ✶✳✽✳ ❱î✐ 0 < a < b ❝â ❝→❝ ❜➜t ✤➥♥❣ t❤ù❝
L(a, b) < M1/3 (a, b), L(a3 , b3 ) < A3 (a, b).
❈❤ù♥❣ ♠✐♥❤✳
d
c
✭✶✳✺✮
❚❤❡♦ ❝æ♥❣ t❤ù❝ ❙✐♠♣s♦♥✱ t❛ ❝â
3 2c + d
3 c + 2d
1
f (x)dx = f (c)(d − c) + f
(d − c) + f
(d − c)
8
8
3
8
3
(c − d)5 (4)
1
f (η),
+ f (c)(d − c) −
8
6480
tr♦♥❣ ✤â
c < η < d.
❈❤♦
c = ln a, d = ln b, f (x) = ex
t❛ ❝â
ln b
ex dx
b−a=
ln a
2 ln a + ln b
ln a + 2 ln b
3
3
eln a + 3e
+ 3e
+ eln b
<
(ln b − ln a)
8
3
a1/3 + b1/3
=
(ln b − ln a).
2
❚ø ✤➙② s✉② r❛ ❜➜t ✤➥♥❣ t❤ù❝ t❤ù ♥❤➜t tr♦♥❣ ✭✶✳✺✮✳ ❚r♦♥❣ ❜➜t ✤➥♥❣ t❤ù❝
t❤ù ♥❤➜t✱ t❤❛②
a, b
t÷ì♥❣ ù♥❣ ❜ð✐
▼➺♥❤ ✤➲ ✶✳✶✳ ❚❛ ❝â ❤➺ t❤ù❝
a3 , b3
t❛ ❝â ❜➜t ✤➥♥❣ t❤ù❝ t❤ù ❤❛✐✳
L(x2 , y 2 )
= A(x, y).
L(x, y)
❈❤ù♥❣ ♠✐♥❤✳
❚❛ ❝â
x2 − y 2
L(x , y ) =
ln x2 − ln y 2
2
2
✭✶✳✻✮
✶✸
(x − y)(x + y)
2(ln x − ln y)
x+y
= L(x, y)
2
= L(x, y)A(x, y).
=
❚ø ✤➙② s✉② r❛ ✤✐➲✉ ♣❤↔✐ ❝❤ù♥❣ ♠✐♥❤✳
❱➼ ❞ö ✶✳✹✳
▲í✐ ❣✐↔✐
❈❤♦
b > a > 0,
❝❤ù♥❣ ♠✐♥❤ ❜➜t ✤➥♥❣ t❤ù❝
b+a
b 2 − a2
<2
ln b − ln a
2
2
.
✳
❚❤❡♦ ✤➥♥❣ t❤ù❝ ✭✶✳✻✮ ✈➔ ❜➜t ✤➥♥❣ t❤ù❝ ✭✶✳✹✮✱ t❛ ❝â
L(a2 , b2 ) = L(a, b)A(a, b) < A2 (a, b).
❚ø ✤â s✉② r❛ ❜➜t ✤➥♥❣ t❤ù❝ ❝➛♥ ♣❤↔✐ ❝❤ù♥❣ ♠✐♥❤✳
✶✹
❈❤÷ì♥❣ ✷✳ ✣➥♥❣ t❤ù❝ ✈➔ ♣❤÷ì♥❣
tr➻♥❤ s✐➯✉ ✈✐➺t ❞↕♥❣ ❧♦❣❛r✐t
◆ë✐ ❞✉♥❣ ❝❤➼♥❤ ❝õ❛ ❝❤÷ì♥❣ ♥➔② ❧➔ tr➻♥❤ ❜➔② ✈➲ ✤➥♥❣ t❤ù❝ ❧♦❣❛r✐t tr♦♥❣
❧î♣ ❤➔♠ sè ❝❤✉②➸♥ ✤ê✐ ❝→❝ ✤↕✐ ❧÷ñ♥❣ tr✉♥❣ ❜➻♥❤❀ ♣❤÷ì♥❣ tr➻♥❤ ❤➔♠ ❈❛✉❝❤②
❞↕♥❣ ❧♦❣❛r✐t ✈➔ ♣❤÷ì♥❣ ♣❤→♣ ❣✐↔✐ ♣❤÷ì♥❣ tr➻♥❤ s✐➯✉ ✈✐➺t ❞↕♥❣ ❧♦❣❛r✐t ❝ò♥❣
♠ët sè ✈➼ ❞ö✳ ❈→❝ ❦➳t q✉↔ ❝❤➼♥❤ ❝õ❛ ❝❤÷ì♥❣ ✤÷ñ❝ t❤❛♠ ❦❤↔♦ tø t➔✐ ❧✐➺✉
❬✶✱ ✸✱ ✺❪✳
✷✳✶ P❤÷ì♥❣ tr➻♥❤ ❤➔♠ ❈❛✉❝❤② ❞↕♥❣ ❧♦❣❛r✐t
❇➔✐ t♦→♥ ✷✳✶
✳
✭P❤÷ì♥❣ tr➻♥❤ ❤➔♠ ❈❛✉❝❤②✮ ❳→❝ ✤à♥❤ ❝→❝ ❤➔♠
❧✐➯♥ tö❝ tr➯♥
R
✈➔ t❤ä❛ ♠➣♥ ✤✐➲✉ ❦✐➺♥
f (x + y) = f (x) + f (y),
▲í✐ ❣✐↔✐
s✉② r❛
f : R → R✱
∀x, y ∈ R.
✭✷✳✶✮
f ❧➔ ❤➔♠ sè t❤ä❛ ♠➣♥ ✤➲ ❜➔✐✱ ❦❤✐ ✤â t❛ ❝â ✭✷✳✶✮✳ ❚ø ✭✷✳✶✮
f (0) = 0, f (−x) = −f (x) ✈➔ ✈î✐ x = y t❤➻
✳ ●✐↔ sû
f (2x) = 2f (x),
●✐↔ sû ✈î✐
k
♥❣✉②➯♥ ❞÷ì♥❣✱
∀x ∈ R.
f (kx) = kf (x)✱ ∀x ∈ R, ∀k ∈ N✳
f ((k + 1)x) = f (kx + x)
= f (kx) + f (x)
= kf (x) + f (x)
= (k + 1)f (x),
∀x ∈ R, ∀k ∈ N.
❚ø ✤â✱ t❤❡♦ ♥❣✉②➯♥ ❧þ q✉② ♥↕♣✱ t❛ ❝â
f (nx) = nf (x),
∀x ∈ N.
✭✷✳✷✮
❑❤✐ ✤â
✶✺
❑➳t ❤ñ♣ ✈î✐ t➼♥❤ ❝❤➜t
f (−x) = −f (x)✱
t❛ ✤÷ñ❝
f (mx) = f (−m(−x)) = −mf (−x) = mf (x),
∀m ∈ Z, ∀x ∈ R.
✭✷✳✸✮
❚ø ✭✷✳✷✮ t❛ ❝â
x
x
x
= 22 f 2 = . . . = 2n f n .
2
2
2
f (x) = 2f
❚ø ✤â s✉② r❛
1
x
=
f (x),
2n
2n
f
∀x ∈ R, ∀n ∈ N.
✭✷✳✹✮
❑➳t ❤ñ♣ ✭✷✳✸✮ ✈➔ ✭✷✳✹✮✱ t❛ ✤÷ñ❝
f
m
m
=
f (1),
2n
2n
❙û ❞ö♥❣ ❣✐↔ t❤✐➳t ❧✐➯♥ tö❝ ❝õ❛ ❤➔♠
f (x) = ax
f✱
s✉② r❛
∀x ∈ R, a = f (1).
f (x) = ax,
❚❤û ❧↕✐✱ t❛ t❤➜② ❤➔♠
∀m ∈ Z, ∀n ∈ N+ .
t❤ä❛ ♠➣♥ ♣❤÷ì♥❣ tr➻♥❤ ✭✷✳✶✮✳
❱➟②
◆❤➟♥ ①➨t ✷✳✶✳
tö❝ tr➯♥
R
f (x) = ax,
✈î✐
a∈R
tò② þ.
❚r♦♥❣ ❜➔✐ t♦→♥ tr➯♥✱ ♥➳✉ t❛ t❤❛② ❣✐↔ t❤✐➳t ❤➔♠ sè
❜ð✐ ❤➔♠ sè
❚❤➟t ✈➟②✱ ♥➳✉ ❤➔♠ sè
f
f
x0 ∈ R t❤➻
✤✐➸♠ x0 t❤➻
❧✐➯♥ tö❝ t↕✐
❧✐➯♥ tö❝ t↕✐
f
❧✐➯♥
❦➳t q✉↔ tr➯♥ ✈➝♥ ✤ó♥❣✳
lim f (x) = f (x0 )
x→x0
✈➔ ✈î✐ ♠é✐
x1 ∈ R
t❛ ✤➲✉ ❝â
f (x) = f (x − x1 + x0 ) + f (x1 ) − f (x0 ), ∀x ∈ R.
❚ø ✤â s✉② r❛
lim f (x) = lim f (x − x1 + x0 ) + f (x1 ) − f (x0 )
x→x1
x→x1
= f (x0 ) + f (x1 ) − f (x0 ) = f (x1 ).
◆❤÷ ✈➟②✱ ♥➳✉ ❤➔♠
f
①→❝ ✤à♥❤ tr➯♥
♠➣♥ ♣❤÷ì♥❣ tr➻♥❤ ❤➔♠ ❈❛✉❝❤② t❤➻
❇➔✐ t♦→♥ ✷✳✷✳
❚➻♠ ❝→❝ ❤➔♠ sè
R✱ ❧✐➯♥ tö❝ t↕✐ ✤✐➸♠ x0 ∈ R
f ❧✐➯♥ tö❝ tr➯♥ R✳
f (x)
①→❝ ✤à♥❤ ✈➔ ❧✐➯♥ tö❝ tr➯♥
R
✈➔ t❤ä❛
✈➔ t❤ä❛
♠➣♥ ✤✐➲✉ ❦✐➺♥
f (x)f (y) = f
x+y
2
, ∀x, y ∈ R.
✭✷✳✺✮
ớ
ứ s r
f (x) x x R
t
x0 + y
2
f (x0 )f (y) = f
tự
tỗ t
x0
f (x0 ) = 0
, x, y R
f (x) 0.
t trữớ ủ
f (x) > 0 x R
x+y
2
ln f
=
õ tữỡ ữỡ ợ
ln f (x) + ln f (y)
, x, y R
2
x+y
2
g
=
g(x) + g(y)
, x, y R
2
g(x) = ln f (x) ữỡ tr t g(x) = ax+b
tr õ
r ừ t õ
f (x) = eax+b , a, b R
ỷ t t
tũ ỵ.
f (x) = eax+b , a, b R tũ
ỵ tọ
ừ t t r t
t
ớ
f (x) 0 f (x) = eax+b , a, b R
số
f
tử tr
R+
tũ ỵ.
tọ
f (x) + f (y)
f ( xy) =
, x, y R+ .
2
sỷ số
f
tử tr
R+
tọ
1
f ( xy) = (f (x) + f (y)), x > 0, y > 0.
2
t
s
x = eu , y = ev g(u) = f (eu ) õ g(u) tử
r ợ ồ u, v R t õ
1
f
eu ev = (f (eu ) + f (ev ))
2
u + v
f (eu ) + f (ev )
f e 2 =
2
g
u+v
2
=
g(u) + g(v)
.
2
tr
R
ứ
ữỡ tr t
g(u) = au + b
tr õ
a, b
số
f (eu ) = au + b.
t
x = eu u = ln x
t õ
f (x) = a ln x + b, a, b R
ỷ t t
tũ ỵ.
f (x) = a ln x + b, a, b R
tũ ỵ tọ
ừ t t r
t
số
f ( xy) =
f
tử tr
R+
tọ
f (x)f (y), x, y R+ .
ớ
ứ ừ t s r
s
f (x0 ) = 0
f (x) 0, x R+
tỗ t
x0 > 0
t tứ s r
f ( x0 y) =
f (x0 )f (y) = 0, y R+ .
f (x) = 0 f (x) > 0 ợ ồ x R+
x = eu , y = ev , f (eu ) = g(u)
õ g(u) tử tr R õ
g u + v = g(u)g(v), u, v R.
r trữớ ủ
t t t
t q ừ t t õ
g(u) 0
ỷ t t
g(u) = eau+b a, b R
tũ ỵ.
f (x) 0 f (x) = ea ln x+b = cxa c > 0 tọ
ừ t t r
f (x) 0
t
f (x) = ea ln x+b = cxa c > 0.
số
f
tử tr
R+
tọ
2f (x)f (y)
f ( xy) =
, x, y R+ .
f (x) + f (y)
ớ
sỷ
f
tử tọ
f ( xy) =
2
1
1
+
f (x) f (y)
x > 0, y > 0.
✶✽
f (x) = 0 ∀x > 0✱ ❦➳t ❤ñ♣
1
1
+
1
f (x) f (y)
=
.
√
2
f
xy
❚ø ✤✐➲✉ ❦✐➺♥ tr➯♥ s✉② r❛
✣➦t
g(x)
g(x) =
1
✳
f (x)
❱➻
f
❧✐➯♥ tö❝ ✈î✐ ♠å✐
❧➔ ❤➔♠ ❧✐➯♥ tö❝ ❦❤✐
a > 0✳
x>0
♠➔
✈î✐ ♠å✐
x, y > 0✱
f (x) = 0 ∀x > 0
t❛ ❝â
s✉② r❛
▼➦t ❦❤→❝✱ t❛ ❝â
g(x) + g(y)
√
g ( xy) =
.
2
❚❤❡♦ ❇➔✐ t♦→♥ ✷✳✸✱ t❛ ❝â g(x) = a ln x + b✳ ❑❤✐ ✤â
1
f (x) =
, ∀x > 0.
a ln x + b
1
◆❣÷ñ❝ ❧↕✐ ♥➳✉ f (x) =
✱ a, b ❧➔ ❝→❝ ❤➡♥❣ sè✳
a ln x + b
◆➳✉ a = 0✱ ①➨t ♣❤÷ì♥❣ tr➻♥❤
b
b
a ln x + b = 0 ⇔ ln x = − ⇔ x = e− a .
a
a=0
❱➟② ♥➳✉
❉♦ ✤â ✤➸
❱➟②
f (x)
t❤➻
f (x)
b
x = x0 = e− a > 0.
1
a = 0 ⇒ f (x) = ✳
b
❦❤æ♥❣ ❧✐➯♥ tö❝ t↕✐
❧✐➯♥ tö❝ ❦❤✐
x>0
t❤➻
f (x) = C ✱ tr♦♥❣ ✤â C = 0 ❧➔ ❤➡♥❣ sè✳ ❚❤û ❧↕✐✱ t❛ t❤➜② ❤➔♠ f (x) = C
t❤ä❛ ♠➣♥ ❝→❝ ✤✐➲✉ ❦✐➺♥ ❝õ❛ ❜➔✐ t♦→♥ ✤➦t r❛✳
✣è✐ ✈î✐ ❤➔♠ ❧♦❣❛r✐t
f (t) = loga t, (0 < a = 1, t > 0)✱
t❛ ❝â ❝→❝ ✤➦❝
tr÷♥❣ s❛✉✿
f (xy) = f (x) + f (y)
✈➔
f
x
y
= f (x) − f (y)✱ ∀x, y ∈ R∗+ ✳
❉♦ ❝â ❝→❝ ✤➦❝ tr÷♥❣ ♥➔②✱ ❤➔♠ sè tr➯♥ ❧➔ ♥❣❤✐➺♠ ❝õ❛ ❝→❝ ♣❤÷ì♥❣ tr➻♥❤ ❤➔♠
t÷ì♥❣ ù♥❣✳
❇➔✐ t♦→♥ ✷✳✻
❤➔♠ sè
f (x)
✭P❤÷ì♥❣ tr➻♥❤ ❤➔♠ ❈❛✉❝❤② ❞↕♥❣ ❧♦❣❛r✐t✮
❧✐➯♥ tö❝ tr➯♥
R \ {0}
❳→❝ ✤à♥❤ ❝→❝
t❤ä❛ ♠➣♥ ✤✐➲✉ ❦✐➺♥
f (xy) = f (x) + f (y),
▲í✐ ❣✐↔✐
✳
∀x, y ∈ R \ {0}.
✭✷✳✾✮
✳
f (x) tr➯♥ ❦❤♦↔♥❣ (0, +∞)✱ ♠✉è♥ ✈➟②✱
x = eu , y = ev ✈➔ f (et ) = g(t)✳ ❑❤✐ ✤â ✭✷✳✾✮ ❝â ❞↕♥❣
❛✮ ❚r÷î❝ ❤➳t t❛ t➻♠ ❤➔♠ sè
x, y ∈ R+ ✳
✣➦t
g(u + v) = g(u) + g(v),
∀u, v ∈ R.
①➨t
✭✷✳✶✵✮
✶✾
❚❤❡♦ ♣❤÷ì♥❣ tr➻♥❤ ❤➔♠ ❈❛✉❝❤② t❤➻ ✭✷✳✶✵✮
∀x ∈ R+ , a ∈ R
f (x) = a ln x,
❜✮ ❚✐➳♣ t❤❡♦ t❛ t➻♠ ❤➔♠ sè
−
x, y ∈ R
t❤➻
xy ∈ R
+
⇔ g(t) = bt
f (x)
tr➯♥ ❦❤♦↔♥❣
✳ ❚r♦♥❣ ✭✷✳✾✮ ❧➜②
y=x
✈➔ ❞♦ ✤â
tò② þ.
(−∞, 0)✱
♠✉è♥ ✈➟②✱ ①➨t
✈➔ sû ❞ö♥❣ ❦➳t q✉↔ ♣❤➛♥ ❛✮
t❛ ✤÷ñ❝
1
1
f (x) = f (x2 ) = b ln x2 = b ln |x|,
2
2
❚❤û ❧↕✐ t❛ t❤➜② ❤➔♠
f (x) = b ln |x|
✈î✐
∀x ∈ R− ,
b∈R
✈î✐
b∈R
tò② þ.
tò② þ✱ t❤ä❛ ♠➣♥ ❝→❝ ✤✐➲✉
❦✐➺♥ ❝õ❛ ❜➔✐ t♦→♥ ✤➦t r❛✳ ❱➟②
f (x) = b ln |x|,
❇➔✐ t♦→♥ ✷✳✼✳
∀x ∈ R \ {0},
❳→❝ ✤à♥❤ ❝→❝ ❤➔♠
f (x)
✈î✐
b∈R
❧✐➯♥ tö❝ tr➯♥
tò② þ.
R+
t❤ä❛ ♠➣♥ ✤✐➲✉
❦✐➺♥
x
y
f
▲í✐ ❣✐↔✐
x
= f (x) − f (y),
∀x, y ∈ R+ .
✭✷✳✶✶✮
✳
✣➦t
y
= t✳
❑❤✐ ✤â
x = ty
✭✷✳✶✶✮
✈➔
⇔ f (t) = f (ty) − f (y)
⇔ f (ty) = f (t) + f (y),
∀t, y ∈ R+ .
❚❤❡♦ ❦➳t q✉↔ ❝õ❛ ❇➔✐ t♦→♥ ✷✳✻✱ t❤➻
∀x ∈ R+ , b ∈ R
f (x) = b ln x,
❚❤û ❧↕✐ t❛ t❤➜② ❤➔♠
f (x) = b ln x,
tò② þ.
∀x ∈ R+ , b ∈ R
tò② þ✱ t❤ä❛ ♠➣♥ ❝→❝
✤✐➲✉ ❦✐➺♥ ❝õ❛ ❜➔✐ t♦→♥ ✤➦t r❛✳ ❱➟②
∀x ∈ R+ , b ∈ R
f (x) = b ln x,
❇➔✐ t♦→♥ ✷✳✽✳
❳→❝ ✤à♥❤ ❤➔♠ sè
f : R → R✱
tò② þ.
❧✐➯♥ tö❝ tr➯♥
R
✈➔ t❤ä❛ ♠➣♥
✤✐➲✉ ❦✐➺♥
f
▲í✐ ❣✐↔✐
x+y
2
2
= f (x)f (y),
∀x, y ∈ R.
✭✷✳✶✷✮
✳
❉➵ t❤➜② ❤➔♠
f ≡0
t❤ä❛ ♠➣♥ ❝→❝ ②➯✉ ❝➛✉ ❝õ❛ ❜➔✐ t♦→♥✳ ❚✐➳♣ t❤❡♦ t❛ ❣✐↔
sỷ
f
ổ trũ ợ
0
tỗ t
x0 R
s
f (x0 ) = 0
ứ
t õ
f (x)f (2x0 x) = f
r
f (x) = 0, x R
f (x) > 0, x R
rữớ ủ
2
x + 2x0 x
2
= [f (x0 )]2 > 0.
t số
g
ữ s
g : R R, g(x) = ln(f (x)), x R.
õ
g
tử tr
g
R
x+y
2
= ln f
x+y
2
= ln
f (x)f (y)
1
= [ln(f (x)) + ln(f (y))]
2
1
= [g(x) + g(y)], x, y R.
2
t số
h(0) = 0
h ữ s h : R R, h(x) = g(x) g(0), x R
h tử tr R ứ t õ
x+y
2
h
r
y=0
=
h(x) + h(y)
,
2
õ
x, y R.
t ữủ
h
x
1
= h(x),
2
2
x, y R.
ứ s r
x, y R.
h(x + y) = h(x) + h(y),
h(x) = x x R
à = g(0) õ
ứ t ữỡ tr t ữủ
ợ
ởt số tỹ tũ ỵ õ t
g(x) = x+à ln(f (x)) = x+à f (x) = ex+à = aex (a = eà > 0).
ỷ t số
f (x) = aex , x R a,
số
a > 0
tọ
ừ
rữớ ủ f (x) < 0,
x R
õ
f (x) > 0, x R
trữớ ủ s r
f (x) = bex ,
x R (b,
số, b
> 0).
f (x) = cex , x R c,
số ỷ t tọ
t số tọ ừ
f (x) = 0, x R
t
f (x) = cex x R (c,
số tử
f :RR
f 2 (x) = f (x + y)f (x y),
ớ
số).
tọ
x, y R.
P (u, v) t x u
u R s f (u) = 0 õ
ỵ
t
t
y
v
P (x, u x) f 2 (x) = 0 f (x) = 0,
sỷ tỗ
x R.
f (x) 0 tọ t sỷ f (x) = 0 x R.
x x
x
P
,
f2
= f (x)f (0)
2 2
2
2 x
f
f (x)
f (x)
= 2 2
>0
f (0)
f (0)
f (0)
x
f
f (x)
2 , x R
ln
= 2 ln
f (0)
f (0)
x
f (x)
, x R, ợ g(x) = ln
.
g(x) = 2g
2
f (0)
ỷ t
ứ t õ
f 2 (x) f (x + y) f (x y)
=
.
, x, y R
f 2 (0)
f (0)
f (0)
f (x + y)
f (x y)
f (x)
= ln
+ ln
, x, y R
2 ln
f (0)
f (0)
f (0)
2g(x) = g(x + y) + g(x y),
x, y R
ứ t õ
g(2x) = g(x + y) + g(x y),
ợ ồ số tỹ
u, v
t
u+v
uv
= x,
= y
2
2
g(u + v) = g(u) + g(v),
x, y R.
ứ t õ
u, v R.
✷✷
❚ø ✭✷✳✷✶✮✱ t❤❡♦ ♣❤÷ì♥❣ tr➻♥❤ ❤➔♠ ❈❛✉❝❤② t❛ ✤÷ñ❝
g(x) ≡ ax✳
f (x)
= eg(x) = eax ⇒ f (x) = f (0)eax ⇒ f (x) = αax ,
f (0)
❚❤û ❧↕✐ t❤➜② ❤➔♠ sè
f (x) = αax , ∀x ∈ R
❝→❝ ❤➔♠ sè t❤ä❛ ♠➣♥ ②➯✉ ❝➛✉ ❝õ❛ ✤➲ ❜➔✐ ❧➔
❤➡♥❣ sè tò② þ✱
a
❱➻ t❤➳
∀x ∈ R.
t❤ä❛ ♠➣♥ ✭✷✳✶✼✮✳ ❱➟②✱ t➜t ❝↔
f (x) = αax , ∀x ∈ R✱
✈î✐
α
❧➔
❧➔ ❤➡♥❣ sè ❞÷ì♥❣✳
✷✳✷ P❤÷ì♥❣ tr➻♥❤ s✐➯✉ ✈✐➺t ❞↕♥❣ ❧♦❣❛r✐t
P❤÷ì♥❣ tr➻♥❤ ❧♦❣❛r✐t ❝ì ❜↔♥ ❝â ❞↕♥❣✿
loga x = m.
❱î✐ ♠é✐ ❣✐→ trà tò② þ
m✱ ♣❤÷ì♥❣ tr➻♥❤ loga x = m ❧✉æ♥ ❝â ♠ët ♥❣❤✐➺♠ ❞✉② ♥❤➜t ❧➔ x = am ✳
m
◆â✐ ❝→❝❤ ❦❤→❝✱ ∀m ∈ (−∞; +∞), loga x = m ⇔ x = a .
❝õ❛
❚r♦♥❣ ♣❤➛♥ ♥➔②✱ tæ✐ tr➻♥❤ ❜➔② ♠ët sè ♣❤÷ì♥❣ ♣❤→♣ ❧♦❣❛r✐t ❣✐↔✐ ♣❤÷ì♥❣
tr➻♥❤ ✤↕✐ sè✳
P❤÷ì♥❣ ♣❤→♣ ✤÷❛ ✈➲ ❝ò♥❣ ❝ì sè ✈➔ ♠ô ❤â❛
❈→❝❤ ❣✐↔✐
•
✳
✳
0 < a = 1
✰ ❉↕♥❣ ✶✿ P❤÷ì♥❣ tr➻♥❤ loga f (x) = b ⇔
f (x) = ab .
0
✰ ❉↕♥❣ ✷✿ P❤÷ì♥❣ tr➻♥❤ loga f (x) = loga g(x) ⇔
f (x) > 0 ❤♦➦❝ g(x) > 0
f (x) = g(x).
t
t
✣➦t t = loga f (x)✳ ❑❤✐ ✤â a = f (x)✱ b = g(x)✱ tø ✤â t❛ t❤✉ ✤÷ñ❝ ♣❤÷ì♥❣
tr➻♥❤ ♠ô✳
❙❛✉ ✤➙② ❧➔ ♠ët sè ✈➼ ❞ö ♠✐♥❤ ❤å❛✳
❱➼ ❞ö ✷✳✶✳
●✐↔✐ ♣❤÷ì♥❣ tr➻♥❤
lg(x3 + 8) = lg(x + 58) +
▲í✐ ❣✐↔✐✳
1
lg(x2 + 4x + 4).
2
✭✷✳✷✷✮
✣✐➲✉ ❦✐➺♥
3
x +8>0
⇔ x + 2 > 0 ⇔ x > −2.
x + 58 > 0
2
x + 4x + 4 > 0
✭✷✳✷✸✮