Giải thích các bước giải:
`1)`
`8/9` `−` `1/72` `−` `1/56` `−` `1/42` `−` `1/30` `−` `1/20` `−` `1/12` `−` `1/6` `−` `1/2`
`=` `8/9` `−` `(1/72 + 1/56 + 1/42 + 1/30 + 1/20 + 1/12 + 1/6 + 1/2)`
`=` `8/9` `−` `(1/8 − 1/9 + 1/7 − 1/8 + ... + 1/2 − 1/3 + 1/2)`
`=` `8/9 − 8/9`
`=` `0`
`2)`
`B` `=` $\frac{5 . 4^15 . 9^9 - 4 . 3^20 . 8^9}{5.2^9.6^19-7.2^29.27^6}$
`=` $\dfrac{5.4^15.9^9-4.3^20.8^9}{5.2^9.6^19-7.2^29.27^6}$ `(2^3)^6`
`=` $\dfrac{3^18.2^29}{2^28.3^18}$
`=` `2`
*Lỗi latex , thông cảm