Đáp án:
Giải thích các bước giải:
a). `8^10` - `8^9` - `8^8`
= `8^8` (8² - 8 - 1)
= `8^8` . 55 $\vdots$ 55
⇒ `8^10` - `8^9` - `8^8` $\vdots$ 55
b). `10^9` + `10^8` + `10^7`
= `10^7` (10² + 10 + 1)
= `10^7` . 111
= `10^6` . 10 . 111
= `10^6` . 2 . 5 . 111
= `10^6` . 2 . 555 $\vdots$ 555
⇒ `10^9` + `10^8` + `10^7` $\vdots$ 555
c). `7^6` + `7^5` - `7^4`
= `7^4` ( 7² + 7 - 1)
= `7^4` . 55
= `7^4` . 5 . 11 $\vdots$ 11
⇒ `7^6` + `7^5` - `7^4` $\vdots$ 11
d). `81^7` - `27^9` - `9^13`
= `3^28` - `3^27` - `3^26`
= `3^26` (3² - 3 - 1)
= `3^26` . 5
= `3^24` . 3² . 5
= `3^24` . 9 . 5
= `3^24` . 45 $\vdots$ 45
⇒ `81^7` - `27^9` - `9^13` $\vdots$ 45