a, Ta có :
\(8^7-2^{18}\)
\(=\left(2^3\right)^7-2^{18}\)
\(=2^{21}-2^{18}\)
\(=2^{18}\left(2^3-1\right)\)
\(=2^{18}.7\)
\(=2^{17}.2.7\)
\(=2^{17}.14⋮14\)
\(\Leftrightarrow8^7-2^{18}⋮14\rightarrowđpcm\)
b, \(10^6-5^7\)
\(=\left(2.5\right)^6-5^7\)
\(=2^6.5^6-5^7\)
\(=2^6.5^6-5^6.5\)
\(=5^6\left(2^6-5\right)\)
\(=5^6.59⋮59\)
\(\Leftrightarrow10^6-5^7⋮59\rightarrowđpcm\)
\(8^7-2^{18}\)
\(=\left(2^3\right)^7-2^{18}\)
\(=2^{21}-2^{18}\)
\(=2^{18}.2^3-2^{18}.1\)
\(=2^{18}.\left(2^3-1\right)\)
\(=2^{18}.7\)
\(=2^{17}.14⋮14\rightarrowđpcm\)
\(10^6-5^7\)
\(=\left(2.5\right)^6-5^7\)
\(=2^6.5^6-5^7\)
\(=64.5^6-5^6.5\)
\(=5^6\left(64-5\right)\)
\(=5^6.59⋮59\rightarrowđpcm\)
