b: \(27D=3^{14}+3^{17}+...+3^{2024}\)

\(\Leftrightarrow26D=3^{2024}-3^{11}\)

hay \(D=\dfrac{3^{2024}-3^{11}}{26}\)

c: \(25E=-5^4-5^6-...-5^{1002}\)

\(\Leftrightarrow24E=-5^{1002}+5^2\)

hay \(E=\dfrac{-5^{1002}+5^2}{24}\)

a ,b

cách 1 : cộng 2 số trong ngặc rồi tính bình thường 

cách 2 : nhân phân phối ra rồi tính nhân chia trước cộng trừ sau

c,d

cách 1 : tính bình thường, nhân chia trc cộng trừ sau

cách 2 : đặt nhân tử ( thừa số ) chung

Cách 1 : \((\frac{6}{11}+\frac{5}{11})\cdot\frac{3}{7}=1\cdot\frac{3}{7}=\frac{3}{7}\)

Cách 2 : \(\frac{6}{11}\cdot\frac{3}{7}+\frac{5}{11}\cdot\frac{3}{7}=\frac{18}{77}+\frac{15}{77}=\frac{33}{77}=\frac{3}{7}\)

Cách 1 dễ rồi nha

Cách 2 : \(\frac{6}{7}:\frac{2}{5}-\frac{4}{7}:\frac{2}{5}=\frac{15}{7}-\frac{10}{7}=\frac{5}{7}\)

Cách 1 tự làm

Cách 2 : \(\frac{3}{5}\cdot(\frac{7}{9}-\frac{2}{9})=\frac{3}{5}\cdot\frac{5}{9}=\frac{1}{3}\)

Cách 1 : ...

Cách 2 : \((\frac{8}{15}+\frac{7}{15}):\frac{2}{11}=1:\frac{2}{11}=\frac{2}{11\cdot1}=\frac{2}{11}\)

`a, 2/7 +(3/7 + 5/7)= 2/7 + 3/7 + 5/7=(2/7 +5/7)+3/7= 1+3/7=7/7+3/7=10/7`

`b, (6/11+5/11)+4/11= 11/11+4/11=15/11`

`c, (5/6 + 7/6)+2/6= 12/6 + 2/6= 14/6= 7/3`

`@ yl`

\(a\) \(\dfrac{2}{7}+\left(\dfrac{3}{7}+\dfrac{5}{7}\right)=\dfrac{2}{7}+\dfrac{8}{7}=\dfrac{10}{7}\)

\(b\) \(\left(\dfrac{6}{11}+\dfrac{5}{11}\right)+\dfrac{4}{11}=\dfrac{11}{11}+\dfrac{4}{11}=\dfrac{15}{11}\)

\(c\) \(\left(\dfrac{5}{6}+\dfrac{7}{6}\right)+\dfrac{2}{6}=\dfrac{12}{6}+\dfrac{2}{6}=\dfrac{14}{6}=\dfrac{7}{3}\)

\(=\dfrac{5}{11}\left(-\dfrac{3}{7}-\dfrac{5}{7}\right)+\dfrac{-8}{7}\cdot\dfrac{6}{11}=\dfrac{-8}{7}\left(\dfrac{5}{11}+\dfrac{6}{11}\right)=-\dfrac{8}{7}\)

\(\dfrac{5}{11}.\left(-\dfrac{3}{7}\right)+\dfrac{5}{11}.\left(-\dfrac{5}{7}\right)+\left(-\dfrac{8}{7}\right).\dfrac{6}{11}\)

\(=\dfrac{5}{11}.\left[-\dfrac{3}{7}+\left(-\dfrac{5}{7}\right)\right]+\left(-\dfrac{8}{7}\right).\dfrac{6}{11}\)

\(=\dfrac{5}{11}.\left(-\dfrac{8}{7}\right)+\left(-\dfrac{8}{7}\right).\dfrac{6}{11}=\left(\dfrac{5}{11}+\dfrac{6}{11}\right).\left(-\dfrac{8}{7}\right)\)

\(=1.\left(-\dfrac{8}{7}\right)=-\dfrac{8}{7}\)

\(\dfrac{5}{11}.\left(-\dfrac{3}{7}\right)+\dfrac{5}{11}.\left(-\dfrac{5}{7}\right)+\left(-\dfrac{8}{7}\right).\dfrac{6}{11}\)

\(=\dfrac{5}{11}.\left(-\dfrac{3}{7}-\dfrac{5}{7}\right)+\left(-\dfrac{8}{7}\right).\dfrac{6}{11}\)

\(=\dfrac{5}{11}.\left(-\dfrac{8}{7}\right)+\left(-\dfrac{8}{7}\right).\dfrac{6}{11}\)

\(=\left(-\dfrac{8}{7}\right).\left(\dfrac{5}{11}+\dfrac{6}{11}\right)\)

\(=\left(-\dfrac{8}{7}\right).1\)

\(=-\dfrac{8}{7}\)

A.3/7

B.3/5

C.5/7

D.11/2

k hộ mình nha!

d)\(\frac{2}{3.5}+\frac{2}{5.7}+....+\frac{2}{97.99}\) 

\(=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+....+\frac{1}{97}-\frac{1}{99}\)

\(=\frac{1}{3}-\frac{1}{99}\)

\(=\frac{32}{99}\)

a)   11/4x(-0,4)x-1,6x11/4

     = -1,1 x-1,6x11/4

    = 1,76x11/4

    = 4,48

b)    6/19x-7/11+6/19x-4/19x-4/11+13/19

     = -42/209+96/3971+13/19

     = -702/3971+13/19

     = 2015/3971

c)     2/5x3/7+-3/7x3/5+3/7

      = 3/7x(2/5+3/5+1)

      = 3/7x(1+1)

      = 3/7x2

      = 6/7

d)      2/3x5+2x5/7+2/7x9+....+2/97x99

      = 1/3-1/5+1/5-1/7+1/7-1/9+......+1/97-1/99

      = 1/3-1/99

      = 32/99

d)=1/3-1/5+1/5-1/7+....+1/97-1/99

=1/3-1/99

=32/99

rut 2 ra khoi mau so ,ben trong la 3/5+3/7+3/11

kết quả là 1/2

\(\frac{\frac{3}{5}+\frac{3}{7}-\frac{3}{11}}{\frac{6}{5}+\frac{6}{7}-\frac{6}{11}}=\frac{3.\left(\frac{1}{5}+\frac{1}{7}-\frac{1}{11}\right)}{6.\left(\frac{1}{5}+\frac{1}{7}-\frac{1}{11}\right)}\)\(=\frac{1}{2}\).

nhiều thế ren giải được ma bik giải xng rồi có dc chi hông?

giải đc k mà

nhiều quá