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Aratati ca numerele urmatoare sunt compuse pentru orice valoare a numarului natural n:
a) A=6 la puterea n + 3 la puterea n + 2 la puterea n+ 1
b) B= 15 la puterea n + 5 la puterea n+1 + 3 la puterea n +5


Răspuns :

[tex]a)~A=6^{n}+3^{n}+2^{n}+1[/tex]

[tex]A=(2*3)^{n}+3^{n}+2^{n}+1[/tex]

[tex]A=2^{n}*3^{n}+1*3^{n}+2^{n}+1[/tex]

[tex]A=3^{n}(2^{n}+1)+1*(2^{n}+1)[/tex]

[tex]A=(2^{n}+1)(3^{n}+1)[/tex]

[tex]=>A~este~compus[/tex]


[tex]b)~B=15^{n}+5^{n+1}+3^{n}+5[/tex]

[tex]B=(3*5)^{n}+5^{n}*5+3^{n}+5[/tex]

[tex]B=3^{n}*5^{n}+5^{n}*5+3^{n}+5[/tex]

[tex]B=3^{n}*5^{n}+3^{n}*1+5*5^{n}+5*1[/tex]

[tex]B=3^{n}(5^{n}+1)+5(5^{n}+1)[/tex]

[tex]B=(5^{n}+1)(3^{n}+5)[/tex]

[tex]=>B~este~compus[/tex]