B= \(24^{54}\). \(54^{24}\). . \(^{2^{10}}\) CMR : B \(⋮\) \(^{72^{63}}\)
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\(24^{54}.54^{24}.2^{10}=\left(2^3.3\right)^{54}.\left(2.3^3\right)^{24}.2^{10}=2^{162}.3^{54}.2^{24}.3^{72}.2^{10}=2^{196}.3^{126}\)
\(72^{63}=\left(2^3.3^2\right)^{63}=2^{189}.3^{126}\)
Mà \(2^{196}.3^{126}⋮2^{189}.3^{126}\Rightarrow24^{54}.54^{24}.2^{10}⋮72^{63}\)
a) \(7^6+7^5-7^4\)chia hết cho 11
\(=7^4\left(7^2+7-1\right)\)
\(=7^4.55=7^4.5.11\)chia hết cho 11
b) \(24^{54}.54^{24}.2^{10}\)chia hết cho \(72^{63}\)
\(=\left(2^3.3\right)^{54}.\left(3^3.2\right)^{24}\)
\(=\left(2^3\right)^{54}.3^{54}.\left(3^3\right)^{24}.2^{24}.2^{10}\)
\(=2^{162}.2^{24}.2^{10}.3^{54}.3^{72}\)
\(=2^{196}.3^{126}\)
\(72^{63}=\left(2^3.3^2\right)^{63}\)
\(=\left(2^3\right)^{63}.\left(3^2\right)^{63}=2^{189}.3^{126}\)
Vì \(2^{196}.3^{126}\)chia hết \(2^{189}.3^{126}\)
\(\Rightarrow24^{54}.54^{24}.2^{10}\)chia hết cho\(72^{63}\)
\(24^{54}.54^{24}.2^{10}=3^{54}.2^{162}.2^{24}.3^{72}.2^{10}=3^{126}.2^{196}\)
ta có: \(72^{63}=9^{63}.8^{63}=\left(3^2\right)^{63}.\left(2^3\right)^{63}=3^{72}.2^{108}\)
ta có: \(\frac{3^{126}.2^{196}}{3^{72}.2^{108}}=3^{54}.2^{88}\)
suy ra \(3^{126}.2^{196}\) chia hết cho \(3^{72}.2^{108}\)
suy ra \(24^{54}.54^{24}.2^{10}\) chia hết cho \(72^{63}\)