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Tính B 

B = 3² - 3⁴ + 3⁶ - 3⁸ +......+ 3⁵⁸

3²B = 3⁴ - 3⁶ + 3⁸ - 3¹⁰ +......- 3⁵⁸ + 3⁵⁹

9B+B = 3⁴ - 3⁶ + 3⁸ - 3¹⁰ +......- 3⁵⁸ + 3⁵⁹ + 3² - 3⁴ + 3⁶ - 3⁸ +......+ 3⁵⁸  

10B = 3⁵⁹ + 3² 

B = \(\frac{3^{59}+3^2}{10}\)

ta có: \(\frac{a}{b}=\frac{27}{99}=\frac{3}{11}\)

\(\Rightarrow11a=3b\)

\(\Rightarrow\frac{b}{11}=\frac{a}{3}=\frac{b-a}{11-3}=\frac{-16}{8}=-2\)

\(\Rightarrow\frac{b}{11}=-2\Rightarrow b=-22\)

\(\frac{a}{3}=-2\Rightarrow a=-6\)

KL: b= -22 ; a= -6

CHÚC BN HỌC TỐT!!!!!!

\(\frac{a}{b}=\frac{27}{99}\Rightarrow a=\frac{27}{99}b\)

Thay \(a=\frac{27}{99}b\) vào b - a = -16 ta được

\(b-\frac{27}{99}b=-16\)

\(\Rightarrow\frac{8}{11}b=-16\)

\(\Rightarrow b=-16:\frac{8}{11}=-22\)

=> a = -22 + 16 = -6

Vậy a=-6,b=-22

so sánh A=3⁴⁵⁰ và B=5³⁰⁰ 

TL: Ta có:

3⁴⁵⁰ = ( 3³ ) ¹⁵⁰ = 27¹⁵⁰

5³⁰⁰ = ( 5² ) ¹⁵⁰ = 25¹⁵⁰

Vì 27¹⁵⁰ > 25¹⁵⁰ => 3⁴⁵⁰ > 5³⁰⁰

học tốt ~~~

\(3^{450}=(3^3)^{150}=27^{150}\)

\(5^{300}=(5^2)^{150}=25^{150}\)

Vì \(27^{150}>25^{150}\)nên \(3^{450}>5^{300}\)

ai do giup minh voi

      \(\frac{3}{4}x-x:\frac{5}{6}=\frac{-7}{8}\)

        \(\frac{3}{4}x-\frac{6}{5}x=\frac{-7}{8}\)

   \(x.\left(\frac{3}{4}-\frac{6}{5}\right)=\frac{-7}{8}\)

                  \(x.\frac{-9}{20}=\frac{-7}{8}\)

                             \(x=\frac{-7}{8}:\frac{-9}{20}\)

                             \(x=\frac{-7}{8}.\frac{20}{-9}\)

                             \(x=\frac{-35}{-18}\)

Vậy \(x=\frac{-35}{-18}\)

3/4x - x : 5/6 = -7/8  

3/4x - 6/5x    = -7/8

x ( 3/4 - 6/5 ) = -7/8

x ( 15/20 - 24/20 ) = -7/8

x . -9/20 = -7/8

        x   = -7/8 : -9/20

        x   = -7/8 . 20/-9 

        x   = 35/18 

a) ĐẶT \(A=\frac{7n-8}{2n-3}=\frac{7n-\frac{21}{2}+\frac{5}{2}}{2n-3}=\frac{\frac{7}{2}\left(2n-3\right)+\frac{5}{2}}{2n-3}=\frac{7}{2}+\frac{\frac{5}{2}}{2n-3}\)

Để A có GTLN\(\Leftrightarrow\frac{\frac{5}{2}}{2n-3}\)có GTLN

\(\Leftrightarrow2n-3\)có GTNN \(2n-3>0\)

\(\Leftrightarrow2n-3=1\)

\(\Leftrightarrow2n=4\)

\(\Leftrightarrow n=2\)

Vậy A có GTLN là 6 khi x=2

b) Ta có: \(\left(5a-3b+12\right)\left(2a-7b+3\right)⋮5\)

MÀ \(\left(5a-3b+12\right)̸⋮5\)(vì 12 ko chia hết cho 5)

\(\Rightarrow2a-7b+3⋮5\)

\(2a-2b-5b+3⋮5\)

MÀ \(5b⋮5\)

\(\Rightarrow2a-2b+3⋮5\)

Và \(40a-10⋮5\)

\(\Rightarrow2a-2b+3+40a-10⋮5\)

\(\Rightarrow42a-2b-7⋮5\left(ĐPCM\right)\)

cảm on bạn nhiều nha Huỳnh Phước Mạnh

\(\frac{2^{76}-2^{74}}{2^{78}-2^{76}}=\frac{2^{74}\left(2^2-1\right)}{2^{76}\left(2^2-1\right)}=\frac{2^{74}}{2^{76}}=\frac{1}{2^2}=\frac{1}{4}.\)

học tốt ~~~