\(\Rightarrow\frac{12-1}{12.1}+\frac{23-12}{12.23}+...+\frac{100-89}{89.100}+x=\frac{2}{3}\)

\(\Rightarrow\frac{12}{12.1}-\frac{1}{12.1}+\frac{23}{12.23}-\frac{12}{12.23}+...+\frac{100}{89.100}-\frac{89}{89.100}+x=\frac{2}{3}\)

Giản ước tử số cho mẫu số ta được: 

\(1-\frac{1}{12}+\frac{1}{12}-\frac{1}{23}+...+\frac{1}{89}-\frac{1}{100}+x=\frac{2}{3}\)

\(\Rightarrow1-\frac{1}{100}+x=\frac{2}{3}\)

\(\Rightarrow\frac{99}{100}+x=\frac{2}{3}\)

\(\Rightarrow x=\frac{2}{3}-\frac{99}{100}\)

\(\Rightarrow x=\frac{-97}{300}\)

mình cũng tính cái bài này rồi thế mà ko ra kq

(11/1×12 + 11/12×23 + 11/23×34 + ... + 11/89×100) + x = 2/3

(1 - 1/12 + 1/12 - 1/23 + 1/23 - 1/34 + ... + 1/89 - 1/100) + x = 2/3

(1 - 1/100) + x = 2/3

99/100 + x = 2/3

x = 2/3 - 99/100

x = 200/300 - 297/300

x = -97/300

Vậy x =-97/300

^_^ ^_^ ☆☆☆

mik biết làm e hk hak

e, = 3,5-(-1):(-0,5)

    = 3,5 - 2

    = 1.5

a) =3/11(-5/12+-7/12)-4/15

= 3/11.(-1)-4/15

=(-3)/11-4/15

=-89/165

a)

\(=\frac{3}{11}\left(\frac{-5}{12}+\frac{-7}{12}\right)-\frac{4}{15}\)

\(=\frac{3}{11}\left(\frac{-12}{12}\right)-\frac{4}{15}\)

\(=\frac{3}{11}\left(-1\right)-\frac{4}{15}\)

\(=\frac{3}{11}-\frac{4}{15}\)

\(=\frac{-89}{165}.\)

5880 nhé

bằng 401582300 nha 

12,65 x X + X x 27,35 = 9

    (12,65 + 27,35) x X = 9

                       40 x X = 9

                              X = 9 : 40

                              X = 0,225

a)12,65 x x + x x 27,35 = 9

   x x ( 12,65 + 27,35 ) = 9

  x x 40 = 9

   x=\(\frac{9}{40}\)

b)11x(x-5)=5x(x+11)

   11x-55=5x+55

   11x-55-5x-55=0

   6x-110=0

   6x=110

   x=\(\frac{55}{3}\)

\(\frac{1}{3\times4}+\frac{1}{4\times5}+\frac{1}{5\times6}+...+\frac{1}{11\times12}\)

\(=\frac{4-3}{3\times4}+\frac{5-4}{4\times5}+\frac{6-5}{5\times6}+...+\frac{12-11}{11\times12}\)

\(=\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+...+\frac{1}{11}-\frac{1}{12}\)

\(=\frac{1}{3}-\frac{1}{12}\)

\(=\frac{1}{4}\)