a/ Ta có: \(8^{n+2}-5^{n+2}+8^n-5^n\)
\(=8^{n+2}+8^n-\left(5^{n+2}+5^n\right)\)
\(=8^n\cdot\left(8^2+1\right)+5^n\cdot\left(5^2+1\right)\)
\(=8^n\cdot65-5^n\cdot26\)
\(=8^n\cdot65-5^{n-1}\cdot5\cdot26\)
\(=8^n\cdot65-5^{n-1}\cdot130\)
\(=\left(8^n-5^{n-1}\cdot2\right)\cdot65⋮65\left(dpcm\right)\)
b/ Tương tự
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