A=12/15 + 28/315

            A=8/9 

1/9xx = 1

x = 1 : 1/9

x= 9

X bằng 9 nhé

             \(\left[\frac{1}{15}+\frac{1}{35}+\frac{1}{36}\right]\cdot x=1\)

                           \(\frac{31}{252}\cdot x=1\)

                                       \(x=1:\frac{31}{252}\)

                                           \(x=\frac{252}{31}\)

\(\left(\frac{1}{15}+\frac{1}{35}+\frac{1}{63}\right)\times x=1\)

\(\Leftrightarrow\frac{1}{9}\times x=1\)

\(\Leftrightarrow x=1\div\frac{1}{9}\)

\(\Leftrightarrow x=9\)

Vậy x=9

_Chúc bạn học tốt_

\(\left(\frac{1}{15}+\frac{1}{35}+\frac{1}{63}\right)\times x=1\)

\(\left(\frac{1}{3\times5}+\frac{1}{5\times7}+\frac{1}{7\times9}\right)\times x=1\)

\(\frac{1}{2}\times\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}\right)\times x=1\)

\(\frac{1}{2}\times\left(\frac{1}{3}-\frac{1}{9}\right)\times x=1\)

\(\frac{1}{2}\times\frac{2}{9}\times x=1\)

\(\frac{1}{9}\times x=1\)

\(x=1:\frac{1}{9}\)

\(x=9\)

(1/15+1/35+1/63)*x=1

1/9*x=1

x      =1:1/9

x      =9

\(\left(\frac{1}{15}+\frac{1}{35}+\frac{1}{63}\right)\times x=1\)

\(\frac{1}{9}\times x=1\)

\(x=1\div\frac{1}{9}\)

\(x=9\)

(1/15+1/35+1/63)×X=1

1/9xX                      =1

X                             =1:1/9

X                             =9

x = 1 : (1/15 + 1/35 + 1/63) 

x = 9

\(\left(\frac{1}{15}+\frac{1}{35}+\frac{1}{63}\right)xX=1\)

\(\frac{1}{9}xX=1\)

\(X=1:\frac{1}{9}\)

\(X=9\)

những ai không biết đừng có linh tinh nghe chưa !!!

X = 9 nha

( 1/15 + 1/35 + 1/63 ) * x = 1

1/9 : x = 1

x = 1 : 1/9

x = 9