10⁹ + 10⁸ + 10⁷ = 10⁷(10² + 10 +1)
=10⁷ * 111
= ((10⁷)/2) *222
= 10⁶*5*222 => 10⁶*5*222 luôn chia hết cho 222
=> 10⁹ + 10⁸ + 10⁷ luôn chia hết cho 222
=> đpcm
Ta có:
\(10^9+10^8+10^7\\ =10^7\left(10^2+10+1\right)\\=5^7.2^7.111\\ =5^7.2^6.222⋮222\left(dpcm\right)\)