Đặt A=a,b(c)
10A = ab,(c)
100A = abc,(c)
100A- 10A = abc,(c) - ab,(c ) = 100a + 10b + c + 0,(c) - 10a - b - 0,(c)
= 90a + 9b
=> 90A = 9 0a + 9b +c
=> A = \(\frac{90a+9b+c}{90}\)
\(a,b\left(c\right)=\frac{ab,\left(c\right)}{10}=\frac{ab+0,\left(c\right)}{10}=\frac{ab+\frac{c}{99}}{10}=\frac{99.ab+c}{990}\)