Răspuns:
Explicație pas cu pas:
[tex]\bf a= \big(3^{21}+3^{20}+3^{19} \big): 39[/tex]
[tex]\bf a= 3^{19} \cdot \big(3^{21 - 19}+3^{20 - 19}+3^{19 -19 } \big): 39[/tex]
[tex]\bf a= 3^{19} \cdot \big(3^{2}+3^{1}+3^{0} \big): 39[/tex]
[tex]\bf a= 3^{19} \cdot \big(9+3+1 \big): 39[/tex]
[tex]\bf a= 3^{19} \cdot 13: 39[/tex]
[tex]\bf a= 3^{18} \cdot 3 \cdot \: 13: 39[/tex]
[tex]\bf a= 3^{18} \cdot 39: 39[/tex]
[tex]\bf a= 3^{18} \cdot 1[/tex]
[tex]\bf a= 3^{18} = \red{\big( 3^{9} \big)^{2} \implies patrat \: perfect}[/tex]
