[tex]2+2 ^{1}+2 ^{2} +2 ^{3}+2 ^{4}+2 ^{5} =2(1+1)+2 ^{2} (1+2)+2 ^{4} *(1+2)=[/tex][tex]2*2+2 ^{2} *3+2 ^{4} *3= 2^{2} (1+3)+ 2^{4} *3=2^{2} *4+ 2^{4} *3= 2^{4}(1+3) [/tex][tex]= 2^{4} *4=2^{4} *2^{2} =2^{4+2} = 2^{6} [/tex]
Se numeşte cub perfect orice număr natural care se poate scrie caputerea a treia a altui număr natural.
a pătrat perfect [tex]a= k^{2} [/tex]
[tex]2 ^{6} =(2 ^{2})^{3}[/tex]este patrat perfect
