1) CMR: $\left ( 3^{2n+1}+2^{n+2} \right )\vdots 7$ ( n thuộc N)
2) CMR: $\left ( 1991^{1993}+1993^{1991} \right )\vdots 12$
1) CMR: $\left ( 3^{2n+1}+2^{n+2} \right )\vdots 7$ ( n thuộc N)
2) CMR: $\left ( 1991^{1993}+1993^{1991} \right )\vdots 12$
1) CMR: $\left ( 3^{2n+1}+2^{n+2} \right )\vdots 7$ ( n thuộc N)
2) CMR: $\left ( 1991^{1993}+1993^{1991} \right )\vdots 12$
1)Ta có: $VT=9^n.3+2^n.4=3(9^n-2^n)+7.2^n=21X+7.2^n\vdots 7$
2)Ta có; $1991^{1993}+1993^{1991}=1991^{1993}+1+1993^{1991}-1=1992X+1992Y\vdots 12$
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