Ai nhanh được k nha :))

Trả lời 

\(A=\frac{11}{12+13}+\frac{12}{13+14}+\frac{1}{14+15}\)

Hay 

\(A=\frac{11}{12+13}+\frac{12}{13+14}+\frac{13}{14+15}\)

mong xem lại hộ cái 

\(\frac{1}{13}+\frac{3}{13}+\frac{5}{13}+\frac{7}{13}+\frac{9}{13}+\frac{11}{13}\)

\(=\frac{1+3+5+7+9+11}{13}\)

\(=\frac{36}{13}\)

\(\frac{1}{13}+\frac{3}{13}+\frac{5}{13}+\frac{7}{13}+\frac{9}{13}+\frac{11}{13}\)

\(=\frac{1+3+5+7+9+11}{13}\)

\(=\frac{36}{13}\)

\(Tacó\)

\(13\equiv1\left(mod4\right)\Rightarrow13^n\equiv1\left(mod4\right)\)

\(\Rightarrow\left(13^n+3\right)⋮4\Leftrightarrow13^n\left(13^n+3\right)\left(13^n+4\right)\left(13^n+1\right)⋮4\left(đpcm\right)\)

Vì n \(\in\) N nên 13ⁿ lẻ \(\Rightarrow\) 13ⁿ + 3 và 13ⁿ + 1 đều chẵn \(\Rightarrow\) (13ⁿ + 3) . (13ⁿ + 1) \(⋮\) 4 \(\Rightarrow\) 13ⁿ . (13ⁿ + 3) . (13ⁿ + 4) . (13ⁿ + 1) \(⋮\) 4

các bạn trả lời giúp mình nhé

a)\(\frac{13}{15}+\frac{13}{35}+\frac{13}{63}+\frac{13}{99}\)

\(=\frac{13}{3.5}+\frac{13}{5.7}+\frac{13}{7.9}+\frac{13}{9.11}\)

\(=\frac{13}{2}\left(\frac{1}{3}-\frac{1}{5}+.....+\frac{1}{9}-\frac{1}{11}\right)\)

\(=\frac{13}{2}\left(\frac{1}{3}-\frac{1}{11}\right)\)

\(=\frac{13}{2}\cdot\frac{8}{33}\)

\(=\frac{52}{33}\)

a) Đặt A= 13/15 + 13/35 + 13/63 + 13/99

A = 13/2 ( 2/15 + 2/35 + 2/63 + 2/99)

A= 13/2 ( 2/ 3.5 + 2/5.7 + 2/7.9 + 2/9.11)

A= 13/2 ( 1/3 - 1/5 + 1/5 - 1/7 + 1/7 - 1/9 + 1/9 - 1/11)

A= 13/2 ( 1/3 - 1/11) 

A= 13/2 . 8/33

A= 52/33  

Dấu \(.\)là dấu nhân 

\(\left(7.13+8.13\right):\left(9\frac{2}{3}-y\right)=39\)

\(\Rightarrow13.\left(7+8\right):\left(\frac{29}{3}-y\right)=39\)

\(\Rightarrow13.15:\left(\frac{29}{3}-y\right)=39\)

\(\Rightarrow195:\left(\frac{29}{3}-y\right)=39\)

\(\Rightarrow\frac{29}{3}-y=195:39\)

\(\Rightarrow\frac{29}{3}-y=5\)

\(\Rightarrow y=\frac{29}{3}-5\)

\(\Rightarrow y=\frac{29}{3}-\frac{15}{3}\)

\(\Rightarrow y=\frac{14}{3}\)

Vậy \(y=\frac{14}{3}\)

~ Ủng hộ nhé . 

P/s : Đúng nha 

(91+104):(29|3-x)=39

195:(29|3-x)=39

29|3-x=195:39=5

x=29|3-5

x=14|3

Bn lớp 5 suy nghĩ đi chứ

Lớp 4 học rồi 

dễ thế mà

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a \(\frac{4}{18}+\frac{5}{13}+\frac{7}{9}+\frac{21}{13}\)

= \(\left(\frac{4}{18}+\frac{7}{9}\right)+\left(\frac{5}{13}+\frac{21}{13}\right)\)

= \(1+2\)

= \(3\)

b \(\frac{4}{3}-\frac{2}{7}-\frac{5}{7}+\frac{2}{3}\)

= \(\left(\frac{4}{3}-\frac{2}{3}\right)-\left(\frac{2}{7}+\frac{5}{7}\right)\)

= \(\frac{2}{3}-1\)

= \(-\frac{1}{3}\)

\(x+\frac{3+\frac{3}{20}+\frac{3}{13}+\frac{3}{2013}}{5+\frac{5}{20}+\frac{5}{13}+\frac{5}{2013}}=\frac{9}{2}\)

\(x+\frac{3\times\left(1+\frac{1}{20}+\frac{1}{13}+\frac{1}{2013}\right)}{5\times\left(1+\frac{1}{20}+\frac{1}{13}+\frac{1}{2013}\right)}=\frac{9}{2}\)

\(x+\frac{3}{5}=\frac{9}{2}\)

\(x=\frac{39}{10}\)

\(x=3,9\)

nham lop roi