Ta có:A=\(5^{n+2}+5^{n+1}+5^n\)
A=\(5^n\cdot5^2+5^n\cdot5^1+5^n\)
A=\(5^n\left(5^2+5+1\right)\)
A=\(5^n\cdot31⋮31\left(đpcm\right)\)
Ta có: \(A=5^{n+2}+5^{n+1}+5^n\)
\(\Rightarrow A=5^n.5^2+5^n.5+5^n\)
\(\Rightarrow A=5^n.\left(5^2+5+1\right)\)
\(\Rightarrow A=5^n.31⋮31\)
Vậy \(A⋮31\)
A = 5n+2 + 5n+1 + 5n
A = 5n . 52 + 5n . 5 + 5n . 1
A = 5n(25 + 5 + 1)
A = 5n . 31
Vì có thừa số 31 trong tích
=> A chia hết cho 31 ( ĐPCM)
\(A=5^{n+2}+5^{n+1}+5^n=5^n\left(5^2+5+1\right)=5^n.31\) chia hết cho 31
;y=-1
; Q(x) = x2 – 9.; R(x) = 3x2 – 4x
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