chuyen chug thah chug so mu

a) ta thấy 

26³⁸=(2.13)³⁸=2³⁸.13³⁸

64²⁵=(2³.8)²⁵=2²⁸.8²⁵

ta dễ dàng nhận thấy: 2²⁸<2³⁸ và 8²⁵<13³⁸ nên: 

26³⁸>64²⁵

>                                

a)>

b)<     

\(\frac{13}{38}\)và  \(\frac{21}{64}\)

Vì \(\frac{13}{38}\)\(>\)\(\frac{13}{39}\)\(=\)\(\frac{1}{3}\)\(;\)\(\frac{1}{3}\)\(=\)\(\frac{21}{63}\)\(>\)\(\frac{21}{64}\)nên   \(\frac{13}{38}\)\(>\)\(\frac{21}{64}\).

Ta có: \(\frac{27}{26}\)= \(\frac{27\times37}{26\times37}\)= \(\frac{999}{962}\).

\(\frac{38}{37}\)= \(\frac{38\times26}{37\times26}\)= \(\frac{988}{962}\).

Mà \(\frac{999}{962}\)> \(\frac{988}{962}\).

=> \(\frac{27}{26}\)> \(\frac{38}{37}\).

ta có 50^40>50^39

        50^39>50^38=)1/50^39<1/50^38

=)50^40+1/50^39>50^39+1/50^38

=)50^40+1/50^39+1>50^39+1/50^38+1

=)A>B

c) \(\dfrac{27}{26}\)và\(\dfrac{38}{37}\)

Ta có: \(\dfrac{27}{26}=1+\dfrac{1}{26}\); \(\dfrac{38}{37}=1+\dfrac{1}{37}\)

Vì \(\dfrac{1}{26}>\dfrac{1}{37}\) nên \(\dfrac{27}{26}>\dfrac{38}{37}\)

c: \(\dfrac{27}{26}-1=\dfrac{1}{26}\)

\(\dfrac{38}{37}-1=\dfrac{1}{37}\)

mà \(\dfrac{1}{26}>\dfrac{1}{37}\)

nên \(\dfrac{27}{26}>\dfrac{38}{37}\)

Ta có : \(26^{50}>25^{50}=\left(5^2\right)^{50}=5^{100}\)

\(124^{33}< 125^{33}=\left(5^3\right)^{33}=5^{99}\)

\(\Rightarrow5^{99}< 5^{100}\Rightarrow125^{33}< 25^{50}\)

\(\Rightarrow124^{33}< 125^{33}< 25^{50}< 26^{50}\)

\(\Rightarrow26^{50}>124^{33}\)

\(26^{50}< 27^{50}=\left(3^3\right)^{50}=3^{150}< 3^{151}\)

Vậy \(26^{50}< 3^{151}\)

\(26^{50}< 27^{50}=\left(3^3\right)^{50}=3^{150}< \)\(3^{151}\)

\(\Rightarrow26^{50}< 3^{151}\)

bài này là 1 bài toán cơ bản , chỉ cần nghĩ một lúc là làm được !