[tex]\displaystyle\bf\\7^{n+2}-4^{n+2}+7^n+4^n=\\\\=7^{n+2}+7^n+4^n-4^{n+2}=\\\\=7^n\times7^2 +7^n+4^n-4^n\times4^2=\\\\=7^n(7^2 +1)+4^n(1-4^2)=\\\\=7^n(49 +1)+4^n(1-16)=\\\\=50\times7^n-15\times4^n=~~~~(Dam~factor~comun~pe~5)\\\\=5\Big(10\times7^n-3\times4^n\Big)~~Este~divizibil~cu~5.[/tex]